Mixtures of polymers for medical use

Process for the preparation of a foamed composition having good compatibility with biological materials consisting of a mixture of vinyl chloride polymer and a polyether-urethane with tertiary amine and/or ammonium groups with the proportion of the polyether-urethane being from 1 to 99 percent by weight, relative to the total mixture, on a blowing agent or a solvent in an inadequate amount to solubilise the total amount of the composition, and in that this paste is then extruded at a temperature below 100.degree. C. to foam said mixture of polymers.