Development of ultralight, tough and hydrophobic polymethylmethacrylate/polyvinylidene fluoride shape memory foams for heat insulation applications

•The plasticization of polyvinylidene fluoride makes foaming temperature window move down by 20 ℃.•Polyvinylidene fluoride microcrystals raise nucleation density by 4.4 times and decrease cell size by more than 50%.•Blend foams offer a lower thermal conductivity of 31.6 mW∙K−1∙m−1 and a higher compressive modulus of 2.7 MPa.•Hydrophobicity, shape memory property and flame retardancy of the blend foams were obviously improved.