A curved, tubular packing casing of unreinforced cellulose having non-uniform wall thickness in cross-section is disclosed. The area of minimum wall thickness lies opposite the area of maximum wall thickness and is situated in the area of the greater, outer radius of curvature. The maximum wall thickness lies in the range from about 50 to 160 .mu.m, and the minimum wall thickness lies in the range from about 10 to 50 .mu.m. The maximum wall thickness is 50 to 800% greater than the minimum wall thickness.