as the polymer sold under the trademark 34 teflon 34 as seen in fig5 the rods such as flap support rod 20 are interconnected by a plurality of links and as shown in fig2 frame 11 39 has four lengths of links indicated by reference characters 26 39 27 39 28 39 and 29 39 these links permit the curtains to be retracted as shown best in fig8 this is accomplished by a pair of air cylinders 30 and 31 which provide retraction means as well as extension means for the retractable curtains cylinder 30 has a rod 32 which is affixed to a clevis 34 the ends of which are held by flap support rod 35 which is the outermost flap support rod of its half of curtain 10 thus as air is introduced into the outer end of cylinder 30 rod 32 moves outwardly pushing clevis 34 and outermost or last flap support rod 35 toward end 36 of curtain frame 11 conversely when air is introduced at inlet 37 of cylinder 30 rod 32 retracts and pulls clevis 34 and its attached last flap support rod 35 back toward the center similarly cylinder 31 and rod 33 work at the same time with the other half of curtain 10 preferably the first and second links such as 38 and 39 or 40 and 41 respectively are of longer length than the third links 42 and 43 all of the remaining links on that half of the curtain are the same length as links 42 and 43 by making the first and second links longer the folded curtain may move into the space occupied by the first and second links and thus the folded curtain is more compact than it would otherwise be if all.