CA1116069A - Solar control film having insulative properties - Google Patents

Abstract

Abstract Composite solar control sheet of the type wherein a transparent-reflective metal layer is coated on a self-supporting transparent polyester foil and protectively covered with a transparent polymeric layer.
The protective polymeric layer is chosen to transmit 80%
or more of the normal room temperature radiant energy.
spectrum (about 4-40 micrometer wave length) so that when the solar control film is positioned inside a window with the protective layer facing the room, heat loss from the room is significantly decreased and the cold weather performance of the film is greatly improved. Among the suitable polymers are polyethylene, polypropylene and polyacrylonitrile.

Description

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SOLAR CONrrROL ~ILM HAVING INSULA~IVE PROPERTIES
-This invention relates to composite solar control sheets and to window units incorporatinK such sheets.
For at least the past several decades many people have striven to develop a window cover or shade which would allow sunli~ht 1 5 v'Lsible wave lengths (0.4-0.7 microrneter) to pass through a glazed window into a room but which would simultaneously reduce glare and exclude sunlight's heat-~enerating near infra-red wave lengths (0.9-2.5 micrometers). Lion, U.S. Patent No.

2,774,021, for example, discloses a wlndow shade in which a transparent or translucent self-supporting cellulosic foil is coated with a transparent~reflective layer of metal on the side adJacent the window, a protective layer of varnlsh or the like optionally being applied over the metal layer to reduce corrosion or mechanlcal damage.
Subsequent reflnements of Lion's window unit (i.e., windowpane plus shade) have included inner storm windowsg where the solar control sheet is sealed or attached to the window ~rame to provide a dead air space between the glass and the shade.
Antonson et al, U.S. Patent No. 3,290,203 describes and clalms a wlndow unit in which a transparent polyester foil is provided with a transparent-reflective metal layer on one face, the metal layer being protectively covered by a transparent protective layer ~.

", ' ' ,, ~ ~ '' ~ . ,' ', (3~;9 which in turn is ad~lered to the inside of a conventional windowpane. This type of wlndow uni'~, which ls slmple, cornpact and convenient, has been found more effective than the Lion window unit in blockin~ the entry of solar-generated near infra-red energy into a room. rrhe transparent protective layer may be either a coating or, if desired, a second poly~ster foll adhered in place, as is shown in, e.g., Windorf, U.S. Patent No. 3,775,226; in the latter case, either of the two polyester foils may be adhered to the windowpane. The adhesive which bonds the solar control sheet to the windowpane may be water-soluble (cf. the Antonson et al patent), pressure-sensitive, pressure-sensitive but water-activatable (cf. Theissen, U.S. Patent 3,6~1,179), or of a "cling" nature (cf. Burger, U.S. Patent 4,095,013).
As will be apparent from the foregoing discussion, work ln the solar control sheet art has been almost exclusively concerned with keeping sunlight's heat and glare from affecting the comfort of those in~ide a room; hence, solar contol sheets have been most widely used in those geographical areas where the outside temperature rarely ~alls below 0C. Studies have shown, however, that windows not only contribute heavily to high *rrhe insulative (or "R" value) is the reciprocal of an "U" value; e.g.~ a U value Or 0.1 is equivalent to an R
value of 10.

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air conditioning energy usage in the summer but also contribute significantly to heat; loss in winter. The thermal conductance (or "Ut' value*) Or a single glazed window typically exceeds 5 kcal/C. hr. m2, whereas a well-insulated wall has a U value less than 0.5 and a well-insultated ceiling has a U value less than 0.2.
Thus, heat can be lost through a conventionally glazed window at a rate over an order of magnitude greater than through insulated walls or ceilings. In cold reglons, attempts to make t~le occupants of a room comfortable in winter have usually involved adding external storm windows (which is not always feasible) and drawing opaque drapes across the face of the window, thereby blocking any view of the outside.
Prior to the present invention, these persons ;
in cold countries who occupied rooms where the windows were protected with solar control sheets (especially where such sheets were adhered to the inner surface of a windowpane) often felt cold in winter for at least two reasons. Solar-originating near infra red energy (0.9-2.5 micrometers) was reflected back outside;
additionally, heat inside the room was transferred to the windowpane by radiation and convection and lost to the outside. About 60% of such loss was caused by internal infra-red energy (wave length range of about 4-40 micrometers) radiating from the skin Or room occupants, as well as from the surface of objects in the room, to .. , : : .: : i . ~

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the solar control sheet, where it was absorbed by the polyester foil adjacent the room, transrnitted by conduction to the metalized layer, further conducted to the windowparle and then radiated to the outside.
5 Although there has been a deslre to Maintain the visual advantages Or solar control sheets whlle improving their poor insulative properties, no rneans for achieving such an objective has previously been provided. Thus, for example, it has been suggested* that the polyester foll could be replaced with polyethylene (which is relatively transparent to infra-red rays), but it has been found impractical to apply a metal vapor coating to polyethylene for use in a solar control sheet~ one or rnore of such properties as handling, adhesion, reflectivity and optical clarity being unsatisfactory.
The present invention is an improved and surprisingly effective form of solar control sheet. ~hen incorporated into a window unit in the outside wall of a room, this new product not only effectively excludes externally originating heat and glare during the summer but also substantially reduces heat loss from internally originating radiation of infra-red energy during the winter.

*Seel e.g., American Institute of Physics Conference Proceedings, No. 25, Efficient Use of Energy, Pat III, p.
292, New York, NY, 1975 . .

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According to a broad aspect of the present invention, there is provided a thin, flexible, self-sustaining transparent reflective sheet material for use in a window unit, said sheet material comprising in laminar combination: a self-sustaining flexible, transparent polyrner film having first and second aces, a transparent-reflective metal layer adhered to the first face of said polymer film, and permanently bonded over said metal layer a flexible, transparent polymeric layer which transmits at least about 80% of infrared radiant energy in the wavelength of 4 to 40 micrometers.
In a preferred embodiment of the invention the polymer film is a biaxially oriented polyethylene terephthalate foil.

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The invention makes it possible to modify awindow unit located in the external wall of' a room, the unlt comprising a plurality of transparent strata including at least (1) a f'irst transparent stratum comprising a rigid windowpane and (2) a second transparent solar control stratum which is located inside the room and which is a flexibLe, unitary mult,i-layer sheet cornprising a transparent-reflective ~etal layer bonded to a transparent polyester foil and protectively covered by a transparent polymeric layer. The improvement lies in making two changes in the solar control stratum, viz., (a) selecting a transparent polymeric layer which transmits at least about ~0% of the normal room temperature radiant energy in the wave length of 4 to 40 micrometers and (b) positioning the polyester foil ad~acent to the windowpane and the protective layer adjacent the room interior, As a result o~ this modification of otherwise conventional solar control sheets, window units o~ the invention not only effectively exclude externally origlnating heat and glare but also display excellent reflectivity to internally originatin~ infra-red energy and thereby signiflcantly improve the insulative efrectiveness o~ the window unit in cold weather. The infra-red transmitting polymeric layer, which should be on the order of 10-50 microme~ers thick to afford adequate protection for the metal layer while minimizin~ absorption of radiant energy, is .
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desirably a polymer of monomers consisting essentially Or lower alkylene monomers or acrylonitrile; however, small amounts of other monomers may be copolymerized wlth the alkylene or acrylonitrile rnonomers, and small amounts of polymers for~ned from such other monomers may be blended with the polyalkylene or polyacrylonitrile to improve handling, processing, etc.
When inrra-red rays pass from a room through the polymeric protective layer, about 85-95% are reflected from the metalized layer back through the protective layer and their heating value thus retalned in the room. The polyester foil, which in previous solar control sheets was located adJacent the room, was quite transparent to the visible spectrum but it transmitted only about 50-60% of the rays in the infra-red spectrum, the remainder being absorbed. Thus, ~or 100 units of in~ra-red energy directed toward the inner face of prior art solar control sheets, no more than about 25-30~ (0.90 x 0.55 x 0.55) was actually returned to the room.
Simple and desirable as the invention may appear in retrospect, those working in the solar control sheet art for decades have failed to r0cognize how it might be arrived at, even though suitable polymeric materials have long been available.
In the accompanying drawing, .: : ~ , - - : , , , . -. - ' , . : ' :

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FIGURE 1 is a cross-sectlorlal vlew of a portion of one type of window unit incorporating the present invention; and FIGURE 2 is a cross-sectional v1ew of a portion of another type of window unit incorporating the invention.
The two fi~ures of the drawlng represent cross-sectional views of two different typea o~ window units; i.e., ~igure 1 illustrates a window unlt Or the type where a composite solar control sheet is adhered to the inner surface of the glass windowpane, while Figure 2 depicts a cross~sectional view of a wlndow unit of the type where the composite solar control sheet is located inside the glass windowpane but is spaced therefrom.
Window units of the latter type include those in which the solar control sheet is either semi-permanently attached to the window frame or mounted on a roller so that it can be moved up and down as necessary. Thus, window units of the type shown in Figure 2 can have the edges of the solar control sheet rnounted in a track at the window edges, sealed to the window frame or held in place with flexible magnets.
Turning first to Figure 1, window unit 10 comprises composite solar control sheet 20 laminated to the inner face Or glass windowpane 30. Solar control : sheet 20 comprises self-supporting polymer layer 21, to one face of which is bonded transparent-reflective metal Ar .... ., " ~ .

6~6g layer 22, which rnay be a vapor-depo~ited layer o~
alurninum, silver, gold, copper, or any other excellent reflector of radiant energy over the solar and infrared spectrum, i.e., 0~3 _ 40 - micrometer wave length. It has been found that this mekal layer shollld have a sheet resistance of less than 20 ohms/square, and preferably less than 10 ohms/square, in order to posæess both adequate transparency to visible liKht rays and good reflectivity of infra-red rays.
Since a thin metallic coatin~ ls subJ0ct to corrosion, mechanical abrasion, or both, it is necessary to protect it with a thin polymeric layer 24, which may be applied by extruding, coatin~ laminating or, preferably, adhering with an extrernely thin layer of adhesive 23. Polymeric layer 24 is selected on the basis of both its ability to protect metal layer 22 and its transparency to inrra-red radiation. It has been demonstrated empirically that the thickness of layer 24 should be at least about 10 micrometers for adequate ~-abrasion resistance, and when the protective layer is applied by coating from a solvent, this is a fairly typical value. When preformed foils of the protective polymeric layer are employed, it is likewise generally desired to employ thicknesses of at least about 10 micrometers to facilitate handling, but thicknesses as great as 25 micrometers or more can be employed successfully. It will be appreciated that the thinner : . , ~: . - , ............... ,~. , ; , ., .. . . . . . ................... .. .
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g protective layer 24, the greater its infra~red transmission. Iikewise~ o~ course, the thinner adhesive layer 23, -the less its absorption of infra-red energy.
Composite solar control sheet 20 is adhered to the inner face Or ~lass 30 by Means Or adhesive layer 26, which may be any o~ those commonly used in the solar control industry today. For example, adhesive layer 26 may be the dried deposit of an aqueous solution of a water-soluble adhesive which is either coated on the inner face of windowpane 30 ~ust before applying solar control sheet 20 or coated on solar control sheet 20 during manufacture, dried and activated with water before appllcation to windowpane 30. Similarly, adhesive layer 26 may be a normally tacky and pressure-sensitive adhesive or any of the so-called "cling" vinyl adhesives.
In order to minimize the deteriorative effect of ultra-violet light on any Or the polymer layers in solar control sheet 20, it is highly desirable to interpose a coating 25, containing a UV absorber, between polymer layer 21 and adhesive layer 26; alternatively, a W
absorber may be incorporated in polymer layer 21 or adheslve layer 26.
In normal use, solar radiation is directed toward face 31 of glass windowpane 30, passing through windowpane 30, adhesive layer 26, UV-absorbing layer 25 (if present) and polymer layer 21. A significant amount of the solar radiation (including rays in both the . . : : :.: . i ., ., :: ; ..

visible spectrum and the near infra-red spectrum) i~ then reflected from metal layer 22 back through polyrner layer 21, UV-absorbing layer 25 (if present), adheslve layer 26 and glass 30, th0reby reducing the light level, heàt and ~lare inside the room in which window unit 10 ls employed~ While glare and heat transmission into the room are ~reatly reduced, sufflclent li~ht i~ trans~ltted into the room through metal layer 22, adhesive layer 23 (if present) and protective polymeric layer 24 to permlt normal activities to be carried on in comfort. Some near infra-red solar energy is absorbed in polymer layer 21, where it is converted to heat and re-transmitted outside by either conduction or radlation through glass 30.
When the temperature outside window unit 10 falls significantly below the temperature inside the room, a different set of factors come into play All objects and persons inside a room may be considered to have a surface temperature of approximately 300K and hence to function as black body radiators, emitting energy in the infra-red spectrum, covering a wave length of approximately 4-40 micrometers. Because of the temperature dif~erence between the opposite sides of window unit 10, there is then a normal tendency to lose heat from the room by the process of radiation. Such infra-red energy is radiated toward the outside, being directed toward inner surface 27 of window unit 10, where it passes first through polymeric protective layer 24, ,, . :, : . ;
` " :: . . , ' '', . . : ' --ll--encounters transparent~reflective metal layer 22, and ls re~lected back through polymer protecti.ve layer 24 into the room. Since the infra-red rays pass through protective layer 24 twice, the amount of radlant energy which is actually returned to the room is ef~ectively the square of the infra-red transmission of layer 24.
Conventional solar control sheets are so mounted on wlndows that a polye.ster foil confronts the room; since polyester polymers have an infra-red transmission value of approximately 0.5-0.6, and slnce about 10% o~ the infra-red ra~iation is absorbed by or transmitted through the metal layer, the amount of energy which is actually returned to the room, when such conventional solar control sheets are used, i5 only about 25-30% of that which is directed toward the window from inside. The balance o~ the energy is absorbed by the polyester foil, where it is con~erted to heat, and trans~itted by conductiorl successively through the metal layer, protective coatin~, adhesive layer, and glass windowpane, where it is lost to the outside. In contrast, solar control sheets of the present invention are mounted so that protective polymeric layer 27 is ad~acent the room and self-supportin~ polymer layer 21 is adjacent windowpane 30, the protective polymer layers of : 25 the present invention are selected to have infra-red transmission values of at least 80%, and preferably 90 or more; solar control sheets of the present invention : . ...... ~ : . . :
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thus return about 65%, ~30% or more of the room-origin infra-red energy to the room.
Attention is now directed to Figure 2, which, as previously noted, depicts a somewhat different type of arrangement. Window unit 40 comprises windowpane 30 and composite solar control sheet 50, the latter bel~g located inside but spaced rrom the inner face of' windowpane 30. Sheet 50 comprises sel~-supportlng polyester foil 51, over one face of which is bonded transparent-re~lective metal layer 52. Protective layer 53, which in thls instance is shown as a self-supporting pre formed polymer foil, is adhered over metal layer 51 by means of adhesive 54. Composite solar control sheet 50 may, and preferably does, incorporate UV-absorbers, as discussed in connection with solar control sheet 20.
Located bet~een windowpane 30 and composite solar control sheet 50 is air space 60. Solar energy strikes ~ace 31 of windowpane 30, radiating through air space 60 to composite sheet 50 in substantially the same manner described in connection with Figure 1. In doing so, the solar-origin lnfra-red (or near infra-red) energy is absorbed in polyester foil 51, whlch is heated thereby. Foil 51 then transfers some of the absorbed heat to the air in space 60 and some to the room by conduction through metal layer 52, adhesive 54 and protective layer 53. If tight peripheral sealing does not exist, additional solar control energy escapes from ~13~

space 60 into the room~ decreasing the effectiveness Or unit 40 in the summer.
Window unit 40 is likewise more ef~ectlve in energy conservation than window unit 10 in the winter for yet another reason. When in~ra-red energy is directed toward face 55, even that en0r~;y which ls converted into heat in layer 53 is not 80 readily transmitted to windowpane 30 and thence outsicle; instead it tends to heat the air in space 60. If glare is o~ no consequence during winter it ls even possible to move composite sheet 50 out of the way during sunny weather keeping lt iIl positlon only during those times when the sun is not shining. On the other hand, a solar control sheet mounted in window Ullit 40 has a greater tendency to impart visual distortion an~ is more subJect to in~ury than when mounted in window unit 10. Further, as has been previously noted, window unit 40 is less efflcient in summer than window unit lO unless care is taken to provide adequate sealing at the edges.
In the following examples, all parts are by weight unless otherwise noted.

A 25-micrometer foil of biaxially oriented polyethylene terephthalate was vapor coated with aluminum to a sheet resistance of approximately 9 ohms/square which resulted in a visible spectrum transmission o~

approxlma~ely 0.18 at 0.55 micrometer wave length. The .
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infra-red reflectance o~ this surface was measured wikh a spectrophotometer and found to be 0.85. The normal emittance, méasured in accordance with ASTM test C4ll5-61, was found to be 0.12. (Theoret'Lçally thé sum of the reflectance and emittance values should equal 1.00. It ls believed that the emittance is significantly rnore reliable than the reflectance value and hence that the infra-red reflectance of' the alumini~ed film may be taken to be o.88.) The alumlnized surface was then coated with a 30.5-micron layer of polyethylene having a density of 0.918 and a melt index of 3.0-3.9 g/10 mln. at 190C.
(commercially available from Union Carbide under the trade designation "DFD-3300"~ by a hot extrusion process, after which the reflectance and emittance measurements were repeated and found to be, respectively, 0.74 and 0.24. An extruded 30.5-micron foil of the same polyethylene was found to have an infra-red transmission value of 0.89. The reflectance and emittance values for a conventional solar control sheet of the type in which a 20 12-25 micrometer layer of biaxially oriented polyethylene -terephthalate is employed in the same effectlYe positlon as the polyethylene in this example, displayed in~ra-red reflectance and emittance values of, respectively, 0.35 and 0.65.

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EXAMPL~ 2 On the l~etalized ~ace of another sample of aluminized polyester foil employed in Example 1, there was coated a 2% methylethyl ketone solution of 95:5 iso-octyl acrylate:acrylic acid pressure-sensitive adhesive and the solvent evaporated to leave a thln (approximately 0.9-micrometer) layer of adhesive welghin~
1.08 g/m2. A 12.7-microrneter foil of biaxially oriented isotactic polypropylene whlch had been sub~ected to corona treatment was then bonded to the adhesive-coated surface using a pair of squeeze rolls at room temperature. Prior to lamination, the polypropylene foil had an infra-red transmlssion value of 0.92, and the norMal emittance of the laminate was found to be 0~25.
Using the data contained in a U.S. Government report entitled "Residential Energy Consumption, Siingle Family Housing", it was assumed that a typical home located in the area of Baltimore, Maryland, has 16.7 square meters of windows and 3.7 square meters of glazed patio doors, all 20~4 square meters being single glazed.
A garage is assumed to be located on the west side of the house, the exterior glass area being distributed on the remaining three sides as follows: north facing, 7.1 m2, south facing, 8.3 m2; east facing, 5.0 m2. Draperies are used on 70% of the glass area and shading on 20%. A
computerized study was then madie to show the energy savings resulting from adhering, to the inside of all , ..... .. .

.. . i . ; , ~,: . , glas~ sur~ac~s, (1) the protect:Lvely coated face o~ a conventiollal solar control sheet and ( 2 ) the polyester film face of the ~olar control sheet of this Example 2.
Results are tabulate~ below:

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solar control sheets, dramatically illustrating the 5 significance Or confronting the lnside o~ the home with an infra-red transmissive layer.
The remarkable winter energy saving resultlnK
from use of the present invention is readily apparent.

Example 2 was repeated except that the tacky acrylate adhesive was replaced with soluble tack-free polyester lamlnat1ng adhesive made by copolymerizing 48 moles terephthalic acid, 20 moles isophthalic acid, 32 moles sebacic acid, 40 moles neopentyl glycol and 60 moles 15 ethylene glycol. ~onding was accomplished by laminating between squeeze rolls heated to approximately 75C. The norrnal emittance of the resultant structure was found to be 0.25.
The solar control sheet of this Example 3 was 20 further processed to make it capable of adhering to a windowpane. First, to the exposed polyethylene terephthala~e surface there was applied a solution of a polyester resin containing, based on solids, 7.5 parts benzophenone UV absorber, and the solvent eavporated to 25 leave about 5.4 grams o~ solids per ~quare meter; the soluble polyester was made by polymerizing 46 moles - - . - , .
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terephthalic acid, 42 moles isophthalic acld, 12 moles sebacic-azelaic acld, 60 rnoles ethylene glycol and 40 moles neopentyl glycol. Next a solution of a 95:5 iso-octyl acrylate:acrylamide copolymer was applied and 5 the solvent evaporated to leave a layer of normally tacky and pressure-sensitive adhesive weighing 2.'7 g/m2. ~n aqueous solution of rnethyl. cellulose was applied over the pressure-sensitive adhesive and the water evaporated to render the surface tack-free but water-activatable for 10 application to a windowpane. When analyzed in accordance with the previously discussed cornputeriæed study, the performance of this solar control sheet was shown to be similar to that of Example 2.

EXAr~PLE 4 Example 3 was repeated, substitutirlg for the polypropylene a 16.5 micrometer foil of polyacrylonitrile having an infra-red transmission value of o.88. The normal emittance of the resultant larninate was 0.30.
Energy-saving performance was calculated to be slight:ly 20 below that of the films of Examples 2 and 3O
To demonstrate the effect of the insulative, or "R", value of solar control sheets which include both a transparent-reflective metal layer and a protective polymer layer of varying transparency to infra-red rays, 25 attention is directed to the following table, which incorporates calculated values:

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It will be apparent that any of the eonventional modifications of solar control sheets may also be incorporated in solar control sheets of the present invention. For example, visible light transmission can be enhanced by applying a quarter wave length coating of high ref'ractive index material to either or both sldes of the rnetalized layer. Colored layers may be incorporated to achieve specific deslred visual effects, etc. Althou~h the abrasion resistance of the exposed polyalkylene 10 metal-protecting layer exceeds that of the exposed polyester f`oil in prior art constructions~ various coatings can be applied to the room-confronting face to further enhance abrasion resistance and facilitate cleaning. Such layers must, however/ be either extremely thin, formed of a substance which is inherently highly transparent to infra-red radiation or both.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A window unit located in the external wall of a room, said unit comprising a plurality of transparent strata and including at least (a) a first transparent stratum comprising a rigid windowpane and (b) a second transparent solar control stratum which is located inside said room and which is a flexible, unitary, multi-layer sheet material comprising a transparent-reflective metal layer bonded to a transparent polymer film and protectively covered by a transparent polymeric layer which is permanently bonded over said metal layer, positioned adjacent the interior of said room and selected from polymers which transmit at least about 80% of the normal room temperature infra-red radiant energy in the wavelength of 4 to 40 micrometers.

2. The window unit of claim 1 wherein the transparent polymeric layer is on the order of 10-50 micrometers thick.

3. The window unit of claim 1 wherein the polymer film of the second stratum is adhered to the windowpane.

4. The window unit of claim 3 wherein the polymeric layer comprises polyethylene.

5. The window unit of claim 3 wherein the polymeric layer comprises polypropylene.

6. The window unit of claim 3 wherein the polymeric layer is polyacrylonitrile.

7. A thin, flexible, self-sustaining transparent reflective sheet material for use in a window unit, said sheet material comprising in laminar combination: (a) a self-sustaining flexible, transparent polymer film having first and second Faces, (b) a transparent-reflective metal layer adhered to the first face of said polymer Film, and (c) permanently bonded over said metal layer, a flexible, transparent polymeric layer which transmits at least about 80% of infrared radiant energy in the wavelength of 4 to 40 micrometers.

8. The sheet material of claim 7 wherein the polymeric layer is a pre-formed foil of polyethylene, polypropylene or polyacrylonitrile, and is adherently bonded over said metal layer by an extremely thin layer of adhesive.

9. The sheet material of claim 8 wherein said polymeric foil is polyethylene.

10. The sheet material of claim 8 wherein said polymeric foil is polypropylene.

11. The sheet material of claim 8 wherein said polymeric foil is polyacrylonitrile.

12. The sheet material of claim 7 wherein a transparent adhesive layer is bonded over the second face of said polymer film.

13. The sheet material of any of claims 7, 8 and 9 wherein the polymer film is a biaxially oriented polyethy-lene terephthalate foil.

14. The sheet material of any of claims 10, 11 and 12 wherein the polymer film is a biaxially oriented polyethy-lene terephthalate foil.