Expansible yarns and threads, and products made using them

A method for producing and using an expansible filamentary sheathed precursor, comprising the steps of:

• passing a multifilamentary central member through a first bath comprising a quantity of heat-expansible microspheres in a liquid binder, such that the liquid binder penetrates between the filaments of the central member, such that the surface of said multifilamentary central member is coated by said heat-expansible microspheres, and such that the microspheres do not substantially penetrate between the filaments of the multifilamentary central member;
• applying a sheath of thermoplastic material to the coated central member, by:
• passing said multifilamentary central member coated by said heat-expansible microspheres through a quantity of a desired thermoplastic material having been heated to a temperature above the activation temperature of the microspheres so as to be melted, and immediately cooling the surface of the thermoplastic material, such that molten thermoplastic material is solidified over the coating of heat-expansible microspheres on the central member without expansion of the heat-expansible microspheres, thus forming an expansible sheathed precursor comprising a multifilamentary central member with a coating of expansible microspheres on the surface thereof, sheathed by the thermoplastic material;
• employing the expansible sheathed precursor in fabrication of a product;
• and
• exposing the fabricated product to heat, causing the sheath of thermoplastic material to soften and the expansible microspheres to expand, such that the expansible sheathed precursor expands, modifying the properties of the fabricated product in a desired manner.