The object of the present invention is a biodegradable polymer network and methods to make it. The polymer network consists of a cross-linked polyester resin, which is composed of hydroxy acid units, structural units derived from an unsaturated bifunctional monomer, and structural units derived from a polyol monomer. The polyester resin is produced directly by a polyoon-densation reaction, after which it is cross-linked to a polymer of high molecular weight The polyester can be co-polymerised with a co-monomer increasing flexibility, or be blended with a reactive macromonomer, which adds elasticity and crosslinking density. The prepared polymer network can be especially used to coat continuous or singular objects made of fibrous, porous, biomass based or inorganic materials, or as a blending component in these, or used to impregnate these in order to induce water durability, barrier properties, elasticity, coherence or mechanical strength.