A curable composition apportioned between at least one Part A and at least one Part B, the Parts sealed within barrier means preventing contamination, the at least one Part A comprising: (i) one or more alkenyl-group containing prepolymers having at least one alkenyl group or moiety per molecule, and the at least one Part B comprising: (ii) one or more SiH-containing prepolymers having at least one Si—H unit per molecule; the composition additionally comprising: (iii) a catalyst for curing by addition of alkenyl-containing prepolymer (i) to SiH-containing prepolymer (ii), wherein prepolymer (ii) is substantially absent from Part A and prepolymer (i) is substantially absent from Part B, methods for preparing the composition, methods for sterilisation thereof, medical and non-medical use thereof, a device incorporating the composition, and a precursor therefor including its sterilisable precursor composition, in particular a terminally sterilisable or terminally sterile composition for medical use, particularly in wound therapy, more particularly as a wound packing material which can be shaped and configured to the shape of a wound, most particularly for application in negative pressure wound therapy (NPWT).