A filamentary strand of a thermoplastic nature is ejected from an ejection nozzle being entrained on a heated medium flow into a stuffing chamber structured on a circulating endless surface moving at a speed slower than the ejection speed and the stuffed filamentary strand is transported, being carried by the endless surface, towards a downstream outlet of the stuffing room in such a way that the yarn mass is gradually compressed during displacement toward the downstream outlet of said stuffing room. During the transportation either a free or a positive cooling is employed. The resultant filamentary strand is provided with random, bulky and round three-dimensional crimps.
