Abstract: Disclosed is a tubular casing of fiber-reinforced regenerated cellulose comprising a film web which is curved to form a tube. The edge regions of the film web, which run parallel to the longitudinal axis, abut or overlap slightly and are sealed by means of a film strip which covers both the edge regions. The film web and the film strip composed of the same material have, in the wet remoistened stage, a breaking strength of about 15 to 30 N/mm.sup.2 and an elongation at break of about 30 to 50% in the longitudinal direction of the web, and a breaking strength of about 15 to 35 N/mm.sup.2 and an elongation at break of about 30 to 50% in the transverse direction of the web. The breaking strength in the transverse direction of the web is equal to or greater than that in the longitudinal direction of the web. On its entire surface facing the film strip, the tubular casing has a substantially gas-impermeable and sealable layer, as has the film strip on the surface which comes into contact with the tubular casing.

Abstract: Disclosed is a biaxially stretched, composite polypropylene film suitable for use as an electrical insulating film, comprising a first layer comprising a first propylene polymer and having a maximum roughness height R.sub.z of its exposed surface of about 0.5 .mu.m, and a second layer contiguous to the first layer comprising a second propylene polymer having a composition different from the first propylene polymer and having a roughness height R.sub.z on its exposed surface ranging between about 0.2 .mu.m and 0.4 .mu.m, with the composite film having a modulus of elasticity of at least about 2000 N/mm.sup.2 in all directions of the plane of the film and a DC dielectric strength of at least about 650 V/.mu.m. Also disclosed is a capacitor comprised of a plurality of these composite films having a metal surface layer and being laminated with one another.