fig1 and fig2 illustrate the preferred embodiment of the window apparatus of the present invention designed to reside at a sloped angle a to a horizontal line h . the apparatus comprises a frame structure 3 having a top end 40 , a bottom end 42 , and two opposing sidewalls 44 and 46 . an upper glazing 2 and a lower glazing 4 are fixed in opposing substantially parallel relation by the frame structure 3 . an insulating shade assembly 50 is mounted between the two glazings 2 and 4 and includes a reflective sheet 5 having two ends 54a and 54b and two side edges 52 . one end 54a of the sheet is secured to a drivable shade roller 6 which is mounted near the frame structure &# 39 ; s top end 40 . the other end of sheet 5 is fixedly secured by any conventional means to the frame structure also near its top end through fastening bar 8 mounted to the frame structure . the shade assembly 50 also includes a tensioning roller 10 which rests on the sheet 5 between the sheet ends for tensioning the sheet in a downward direction such that the sheet has a substantially u - shaped configuration when extended . when the shade assembly is in the extended position the upper leg of the u - shaped sheet configuration defines an upper portion 56 of the sheet and the lower leg of the u - shaped configuration defines a lower portion 58 of the sheet . the insulating shade assembly also comprises a moveable or first support means 22 affixed to the upper portion 56 of the sheet parallel to the axis of the shade roller 6 so as to extend from and retract to the shade roller with the sheet . the first support means preferably consists of a plurality of elongate bars of a length sufficient for their ends to engage and slide on two slideways 20 when the upper portion of the sheet is being extended or retracted . slideways 20 are secured to frame structure 3 on opposing walls 44 and 46 . first support means 22 is constructed so as to support the sheet 5 in a substantially flat plane when extended . shade roller 6 is mounted sufficiently above than the slideways for the ends of the first supporting means to land smoothly on the slideways whenever the sheet is being extended . the tensioning roller 10 is of a length sufficient for its ends to engage and roll on guideways 12 , which are also secured to the frame structure on opposing sidewalls . the guideways are in a plane generally parallel to and at a spaced distance above the lower glazing . the guideways may also support and seal the side edges of the lower portion 58 of the sheet if desired . a second or stationary support means 14 is preferably provided and configured to support the lower portion 58 of the sheet 5 in a plane generally parallel to and at a spaced distance above the lower glazing 4 . support means 14 should be configured to allow maximum light transmission through the window . the stationary support means may be one or a plurality of wires , bars or the like spanning crosswise 14a or lengthwise 14b the window apparatus as best shown in fig2 . support means 14 may be strung from opposing frame side walls 44 and 46 and / or from fastening bar 8 at the top end of the frame structure to sealing bar 18 at the bottom end , or simply lay on the lower glazing 4 . first support means 22 , stationary support means 14 and the tensioning roller 10 cooperate to hold sheet 5 in the illustrated u - shaped configuration such that three insulating air spaces 16 , 24 and 26 are defined between the glazings . some sagging of the sheet intermediate the supports may be tolerated as long as the air spaces are substantially preserved . the amount of sagging mainly depends upon the spacing of the supports , the weight of the tensioning roller relative to the weight of the sheet and the sloped angle of the window . when some sacrifice in insulating value is acceptable , the stationary support means may be removed and the lower portion of the sheet allowed to rest directly on the lower glazing . this would result in a decrease of about 20 % in the overall insulating value of the window apparatus with the shade assembly extended . further , the guideways may also be removed and the tensioning roller allowed to be supported by the lower glazing . the ends of the tensioning roller could also have a ring like bulge so that the main portion of the tensioning roller does not abrade the sheet by pressing it against the lower glazing . when the prime objective is shading , the reflective sheet may be suitably of a light color material or made of a more or less optically opaque film with a reflective layer . however , when thermal or radiative insulation is the main objective , the reflective layer should be at the surface of the sheet and have a low emissivity coefficient at least in the far - infared range , i . e ., low absorbance and low re - emittance of infared radiation . the lower the coefficient , the better ; the maximum acceptable is 0 . 6 . further , at least one of the two larger opposing boundary means of a defined air space must have a low emissivity coefficient . the boundary means with the low emissivity coefficient may either comprise the surface of the upper or the lower portion of the sheet , or the inner surface of the glazing facing either the upper or the lower portion of the sheet . for reasons of aesthetics , a low emissivity coating may be objectionable on the visible face of the sheet , in which case a glazing with a low emissivity could be used on the opposite face of the defined air space . the sheet may also be more or less optically translucent in the visible range to meet a desired degree of shading . the low emissivity coating is generally achieved by depositing metal atoms on the surface of a translucent plastic film by vacuum metallizing or sputtering techniques . the metallic coating is in most cases very sensitive to abrasion and can be scratched or marred easily . the special way of this invention in which the tensioning roller lays the sheet onto the stationary support means without relative sliding motion of the sheet to the stationary support means ensures that virtually no abrasion is produced . at less than a fully extended position , the roller shade is used mainly for shading and the thickness of the defined air spaces is less important . however , when used for insulation , sheet 5 is normally fully extended and it is more important to maintain relatively uniform air space thickness , meaning higher tension is required in sheet 5 . this is not easily achieved at a shallow slope , for instance below 20 degrees . in this case it is preferred to allow tensioning roller 10 to bottom out , hanging nearly vertically , immediately past the rounded lower top edge of sealing bar 18 , so that the full weight of tensioning roller 10 is used for tensioning sheet 5 . in practice , it has been found that the minimum window sloped angle is about 15 degrees with materials generally used in the trade such as anodized or enameled aluminium sliding ways . the sliding surfaces of slideways 20 should be smooth and hard enough for the coefficient of friction to be as low as economically feasible . anodized or enameled aluminium is acceptable . first supporting means should be made of a lightweight but rigid and hard material for stiffness and a low coefficient of friction . a good candidate for this is aluminium alloy 7075 in the t6 temper . their ends may also be coated or tipped with nylon or any similar low friction material . in order to maintain tension in sheet 5 , shade roller 6 must be stopped before tensioning roller 10 bottoms out at the bottom end of the window , this may be done in many ways known to the trade , but the preferred way , which is also a novel , is to utilize a pawl 28 ( see fig4 ). the pawl is normally held recessed in shade roller 6 by the innermost wrap of sheet 5 and extends out by means of gravity or a spring when released by the innermost wrap of sheet 5 unwinding from shade roller 6 . shade roller 6 stops when pawl 28 hits stop 30 . pawl 28 is tucked back inside shade roller 6 by sheet 5 as the innermost wrap of sheet 5 is wound back on shade roller 6 . when the shade roller is driven by a motor , stop 30 may be replaced by a limit switch for stopping the motor when sheet 5 is fully extended . as shown in fig2 the upper portion of sheet 5 may be made wider than the lower portion , and of a width sufficient for its side edges to engage and rest on slideways 20 for supporting and sealing the side edges of the upper portion of the sheet when the sheet is extended . fig3 is an enlarged partial end view of shade roller 6 and shows the first support means 22 affixed to sheet 5 at spaced intervals . support means 22 is shown to comprise multiple members shaped with a thin arcuate cross - section so as to conform to the shade roller and spaced so as not to overlap each other . although specific embodiments of the present have been described in detail above , it is to be understood that this is only for purposes of illustration . modifications may be made to the described structures to adopt this invention to particular insulating or shading applications without departing from the scope or spirit of the attached claims .