A tubular casing for use with food products which includes knitted stockinette, longitudinal threads and circumferential spiral threads that are held to stockinette by stitches located along the length of the casing. Each thread comprises an elastic thread formed from an inextensible yarn spirally wrapped around the outside of a rubber thread. As thread is stretched, the rubber thread extends and the helix angle of the spirally wrapped yarn reduces to the point where the yarn approximates a straight line. The inextensible yarn resists further stretching beyond this point. This point is the elastic limit for thread and it can be adjusted by varying the helix angle during manufacture of the elastic thread. Threads therefore allow the casing to be filed to a predetermined maximum diameter and result in the filled casing having a constant diameter throughout its length.