Abstract: A method for preparing a solid composite material comprising a structural polymer matrix and a thermo-responsive hydrogel involves forming a substantially homogeneous blend of a cross-linkable compound and monomer, oligomer or polymer particles in a blended aqueous liquid, inducing the cross-linkable compound to cross-link to form the thermo-responsive hydrogel and forming the structural polymer matrix from the structural polymer by a further induction means, wherein the resulting solid composite material provides a textile or membrane which presents a thermally insulating layer, through which air and/or liquid water cannot easily pass at low temperatures, but which also provides a more open structure at higher temperatures so that air and moisture vapor can pass through the textile or membrane.