fig1 shows storm window 10 comprised of flexible transparent sheet 12 and an encircling outer portion 14 of generally tubular cross section . transparent sheet 12 is secured to encircling outer portion 14 by conventional means such as cementing or heat sealing . window 10 is shown positioned within the window opening of building wall 16 and sill 18 . inflation of the storm window is accomplished by means of valve 20 . fig2 shows a cross sectional view of the installed storm window taken along line 2 -- 2 of the fig1 presentation . in fig2 outer portion 14 of storm window 10 is seen to be pressing against window opening sidewall 17 . sidewall 17 is shown as extending from window frame 22 to inside wall 16 of the building . in the fig2 implementation frame 22 is intended as typifying aluminum frame window construction where frame member 22 is secured by nails or screws to stud member 24 . exterior insulation board 26 is faced with brick wall 28 . inside wall member 16 and sidewall 17 can typically be of plaster , plasterboard , or wood paneling . window frame 22 contains lower window sash 30 which is glazed with glass pane 32 . the bottom side of upper window sash 34 is shown as being placed outwardly of lower sash 30 . fig2 shows that there is a second transparent sheet 13 placed parallel to and behind first transparent sheet 12 . injection of pressurized air into tubular outer member 14 does two things . first , the pressurized air causes outer member 14 to enlarge in cross section and expand outward so that the outer periphery of member 14 presses against window sidewall 17 . second , the pressurized air is allowed to flow into the cavity between first sheet 12 and second sheet 13 . pressurizing the space between sheets 12 and 13 both keeps the film taut thus precluding transparency destroying wrinkles and at the same time establishes an improved insulation barrier . communication between the inside of tubular member 14 and the cavity between transparent sheets 12 and 13 is shown in fig3 . ports 36 along the inward facing wall of tubular member 14 allows a gradual flow of air both into and out of central cavity 38 . fig4 shows one form of valve which may be used for inflating the storm window . a short section of flexible tubing 40 is attached to the sidewall of tubular outer member 14 . attachment may be by cementing , vulcanizing or a parametric heat seal depending on the materials used . the nozzle of the pressurizing cannister ( not shown ) is inserted in the end of tube 40 and the storm window inflated . after inflation , the nozzle would be removed and plug 42 inserted in the end of tube 40 . plug 42 has transverse serrations on its outward extending end so that it does not slip out of tube 40 after insertion . it is usually found expedient with this type of valve to include loop 44 between plug 42 and tube 40 so that the pressure retaining plug does not get lost . in some implementations it may be desirable to use pressurizing valves of the type used in basketball bladders or bicycle inner tubes . fig5 shows a configuration of my invention which is generally similar to that shown in fig1 . however , there is added to the fig1 configuration a pair of flexible tubular supports 50 and 52 . the ends of tubular support 50 are attached to outer member 14 at junction points 54 and 55 . attachment is such that there is communication between the interior of tubular outer member 14 and the interior of tubular support 50 . the same arrangement applies at junction points 56 and 57 where support 52 attaches to the inside edges of outer element 14 . inclusion of horizontal and vertical tubular support members 50 and 52 provides additional outward thrust on the midspan portions of the storm window . this results from the fact that pressurization of tubular supports 50 and 52 cause them to assume a rigid , straight position . the reason that tubular support members tend to lengthen when pressurized is shown in fig9 which is an enlarged cross sectional view of a segment of tube 50 . there are a multiplicity of regularly spaced cross axis indentations along tube 50 . one such indentation 60 is shown in fig9 . since there is less wall thickness stock at indentation 60 than at wall section 58 in the tube , pressure on the inside of the tube tends to make the tubular member expand lengthwise . tubing of this type can be readily obtained as a standard stock item . the choice as to whether horizontal and vertical tubular supports are needed is somewhat a function of window size . small windows do not require any midspan support . large storm windows may need more than the single horizontal and vertical support shown in fig5 . fig6 shows in partial cross section , an alternate implementation of the storm window . there is shown a cross section of tubular outer member 14 . member 14 has on its window frame contacting edge , a strip 62 of tacky material which is firmly attached to member 14 . strip 62 can be either a gummy plastic substance that adheres to the window frame or a strip of plastic having surface gripping striations on its outermost side . along the inward facing edge of tubular outer member 14 there is lipped groove 64 . into this groove 64 is placed a self supporting sheet 66 . self supporting sheet 66 may , for example , be made of a transparent plastic material that is approximately one eighth inch thick . alternatively , the self support structure shown in fig7 may be used . the fig7 implementation includes tubular outer member 14 having groove 64 along the inside edge . inserted in groove 64 is metallic strip 68 . metallic strip 68 may be die formed as shown . strip 68 will extend around the periphery of a transparent sheet 70 , serving to keep sheet 70 stretched out taut as it is held between the opposing faces of metallic strip 68 . sheet 70 may be cemented in place in strip 68 . metallic strip 68 also provides a supporting structure against which the tubular outer member can exert force when pressing against the window frame . fig7 also illustrates another means for filling the outer tubular member . instead of pressurizing the inflatable window with air , fig7 shows the result achieved when a foam - in - place plastic filler 72 is used . with the fig7 implementation , a permanent custom fitted storm window is achieved since the tubular outer member 14 will expand everywhere to fit the configuration of the window frame . then , once the foam - in - place plastic has set up , the storm window assembly will permanently retain the shape originally assumed . fig8 shows a preformed right angled elbow 74 which can be inserted into the corners of tubular outer member 14 during the fabrication phase . elbows 74 assist the inflated storm window to remain snuggly in the corners of the window frame . elbow 74 can be fabricated from a polymeric resinous material that readily bonds to the material used in making tubular outer member 14 stock . the illustrated embodiments of my invention have been described in considerable detail . it will be understood that modifications may be made to the cross sectional configuration of the tubular outer member and in the specific form of valve unit used to inflate the window without departing from the spirit of my invention . also various means can be used to inflate the storm window unit .