Abstract: The body of a mattress comprises a cocoon thread bundle of long fibers formed by reeling cocoon threads off cocoons and separating them one from another. The body the mattress also has inner layers sandwiching the bundle. The body is quilted at appropriate positions and covered by a suface cloth made of woven fabric, and the periphery of the body is fastened by a retention cloth. The mattress has touch different from, for example feather mattress and serves to reduce yarn breakage of the cocoon long-fibers which are used as the stuffing. The stuffing can be easily produced without fail by a process comprising the steps of reeling cocoon threads off boiled cocoons and winding them around a take-up reel, fusing the wound cocoon threads at appropriate positional, and cutting the fused bundles.