Abstract: In a process for impregnating a reel of thread in the form of a spool with a liquid resin composition, the thread is arranged on a perforated rigid mandrel so as to form a uniform reel in which the volume of open space approximately corresponds to the desired volume of resin to be impregnated, each spool is then gripped and completely sealed against resin leakage from its ends and, finally, the composition is injected under pressure into the interior of the perforated mandrel whereby there is a homogeneous loss of pressure from the mandrel to the spool's entire exterior curved surface and the resin diffuses uniformly to fill all voids through the spool.