A new hot-melt adhesive formulations having improved processability and that are easily processable even with processes at high speed and in particular with Spraying or Fiberization processes. Said hot-melt adhesive formulations comprise, as their main polymer component, at least one isotactic metallocene butene-1 polymer composition, that has a low viscosity, and that has a substantially bimodal composition, directly obtained during polymerization, in two consecutive and separate reaction steps, where the first polymer (polymer A) of said compositionally bimodal polymer composition is an isotactic butene-1 homopolymer or an isotactic butene-1 copolymer with another olefin, while the second polymer (polymer B) is an isotactic copolymer of butene-1, with another olefin, with a chemical composition obviously different from A, qualitatively and/or quantitatively; said hot-melts further comprising a viscosity modifier that is not solid at room temperature.