Welt cords or sometimes called piping come in a variety of materials & thickness including braided, plastic, foam and double welt cords each has its own characteristics and uses.
1/8" Solid Plastic Welt Cord
1/8” Hallow Plastic Welt Cord
5/32 Foam / Poly Welt Cord Indoor Outdoor Piping
Welt Cord Braided White
4/32” Double Welt Cord Braided White