PURPOSE: To retain compression properties, improve workability in the field and lighten the weight of filaments by forming the filaments having a specified outer periphery diamer and a specified hollow rate into a continuous and/or discontinuous hollow shape.

CONSTITUTION: Loops are formed with a number of filaments made of a thermoplastic resin, and the loops are mutually adhered at points. Each filament has 0.1 to 7mm of an outer periphery diameter and 5 to 80% of a hollow rate and is formed into a continuous and/or discontinuous hollows shape. A polyolefin polymer, a polyester polymer, a polyester elastomer and the like such as polyethylene, polypropylene, etc., are used as a thermoplastic resin. When the outer periphery diameter of the filament exceeds 7mm, the weight of the filaments is increased, and workability in the field also becomes worse. On the other hand, the hollow rate less than 5% has little effect to lighten the weight of the same and, when it exceeds 80%, a compression strength is reduced. The resin is spun from a nozzle of an extruder to be dropped under its own weight. While the filaments are in a molten state, they are allowed to adhere to one another and cured, whereby compression properties are made better.