1,017,398. Tubular films. I.C.P.M. INDUSTRIE CHIMICHE PORTO MARGHERA S.p.A. Sept. 5, 1962, No. 34011/62. Heading B5B. A device 8 for adjusting the diameter of tubular films made by inflation comprises an injector 1 supplied with compressed gas via tube 7, a variable pressure chamber 2 communicating with the interior of the bubble 6 by a connecting tube 3-3<SP>1</SP>, and a revolvable pierced mask 4 coaxial with the injector chamber and integral with a skid or shoe 5 resting against the exterior of the bubble 6. Chamber 2 has a hole 102 the aperture of which can be increased or decreased by rotation of mask 4, fitted with a correspondong hole 104, about the surface of the shell 203. Shell 203 is carried by arm 11 which is revolvably supported by support 110, which, through location screws 10, enables the inclination of arm 11 to be adjusted. In operation, the melt enters nozzle 30 via tube 9 and is extruded to form a bubble 6, inflation gas being supplied via tube 7, chamber 2 and tube 3-3<SP>1</SP> to the bubble interior. A proportion of the gas leaks out via holes 102 and 104 which normally partially overlap. Should the bubble diminish in volume the skid 5 falls, partially or wholly closing the leak and thus increasing the pressure of the gas supplied to the interior of the bubble. Should the bubble increase in volume the skid 5 rises, further opening the leak and thus reducing the pressure of the gas supplied to the tube interior. Skid 5 may be arranged to fall under its own weight or by the action of springs. Bubble diameter may be varied by altering the inclination of the supporting arm 11, and the sensitivity of the apparatus, i.e. the promptness with which it intervenes may be adjusted by inclining the shoe arm or by adjusting the pressure exerted by the shoe arm on the tubular film.