The invention relates to a heat-sealable biodegradable packaging material. The packaging material comprises a fibrous substrate and one or more polymer coating layers extruded onto the substrate. According to the packaging material, the packaging material includes at least one polymer coating layer containing polylactide and at least about 1% by weight of terpene phenolic resin blended therewith. The invention further relates to a heat-sealed product package made from the packaging material, as well as uses of the resin as blends with polylactide in extrusion coating, for improving line speed and neck-in in extrusion, adhesivity of the coating to the fibrous substrate, and heat-sealability of the coating.