Abstract: A cylindrical stabilizing means (stabilizer) for resin bubbles useful to perform shaping of tubular films without causing the fluctuation or breakage of resin bubbles even in case where a take up velocity of the tubular film is relatively large, cooling of tubular body of molten resin extrudated from a die is not sufficient or amount of extrudate from a die is relatively large, is provided. Said stabilizing means has penetration holes on the circumferential wall close to the annular slit 16 of die, which communicate with an opening of the tip of the means, and also has continuous deep grooves of a depth of 0.5 mm or more extending from the portion of the circumferential wall close to said annular slit to the opening of the tip, which grooves are formed on the whole outer circumferential wall having fine concave and convex engraved patterns of the difference of height or depth of from 0.1 mm to 0.5 mm.

Abstract: Tubular films having superior mechanical properties and extremely small deviation in thickness can be produced according to a method and an apparatus in which a means of downwardly tapered hollow inverted-truncated-conical shape is placed on the top of an annular die and used as a means for stabilizing bubbles of olefinic polymer synthetic resins which are extruded from the annular die in an air-cooling inflation process with a take-up speed of about 5 m to 50 m per minute.