Abstract: A process for continuously dyeing or chemically treating textile staple length fibers having thermoplastic properties while conveying the fibers in a desired path of travel wherein the fibers are impregnated by passage through a liquid dye or chemical applicator and subsequently compressed and advanced in compressed form into and through a confined heating zone for reaction of the dye or chemical with the fibers, and wherein the fibers are preheated prior to their compaction at a temperature below their second order transition point but above the reaction temperature of the dye or other chemical applied thereto to compact and reduce the bulk of the same before their compression and delivery into the confined heating zone.