Heat-sealable biodegradable packaging material, a method for its manufacture, and a product package made from the material

A heat-sealable biodegradable packaging material, its manufacturing method and a product package formed thereof, where the packaging material comprises a fiber substrate, an inner polymeric coating layer against the fiber substrate, which contains polylactide and a biodegradable polyester that is blended therewith to improve the adhesion between the inner coating layer and the fiber substrate, and an outer coating layer that constitutes the outer surface of the material and contains polylactide and a biodegradable polyester that is blended therewith to improve the heat sealing ability of the layer, the portion of polylactide in the inner layer than that in the outer layer. The inner and/or outer coating layers can further have blended therewith a small amount of acrylic copolymer that improves the adhesion and/or heat sealing ability. The coating layers can be introduced onto the fiber substrate by extrusion or coextrusion.