Described is a process for producing segmented polyurethanes having improved processing characteristics in the melt state and an efficient spinning process based thereon to form highly elastic, fine linear density elastane yarn and filament having improved mechanical and thermal properties by using hydroxyalkyl-terminated polysiloxanes in combination with specific crosslinking-capable polyisocyanates in the reaction of long-chain high molecular weight polyhydroxy compounds with organic diisocyanates and low molecular weight diols and also optionally further auxiliary and additive substances in the melt.