Curable polyurethane based resin for use in additive manufacturing

A liquid photopolymerizable polyurethane based resin having a viscosity of less than 15 Pa·s measured according to ASTM D445-11a at 35° C. which is polymerizable by exposure to actinic radiation, said resin comprising a) functionalized polyurethane compounds wherein the compounds are functionalized with reactive ethylenically unsaturated moieties, b) at least one reactive diluent compound having at least one ethylenically unsaturated functional group and c) at least one photo-initiator, wherein the at least one reactive diluent compounds comprise a diluent selected from (i) isobornyl acrylate (IBOA), isobornyl methacrylate (IBOMA), tertisobutyl cyclohexyl acrylate (TBCHA), 4-tert-butyl cyclohexyl methacrylate (TBCHMA), 3,3,5 trimethyl cyclohexanol acrylate (TMCHA), trimethylcyclohexyl methacrylate (TMCHMA), dihydrodicyclopentadienyl acrylate (DCPA) and combinations thereof or (ii) hydroxyethylmethacrylate (HEMA), hydroxypropyl methacrylate (HPMA), acrylic acid, methacrylic acid, N-vinyl-N-methylacetamide, acryloylmorpholine, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate and combinations thereof, wherein at least 60 wt % of the functionalized polyurethane compounds have a number average molecular weight in the range of 3000-12000 g/mol, wherein the amount and choice of functionalized polyurethane compounds and reactive diluent compounds is such that by exposing actinic radiation to the resin, phase separation occurs during photopolymerization of the resin.