A composition comprising a continuous thermoplastic polymer matrix having a melting point greater than 110° C. and, distributed within the matrix, particles of hydrophilic natural fiber material having a sieved size of less than 1.0 mm, the weight ratio of the thermoplastic polymer to the wood particles being from 99:1 to 35:65. An improvement in biodegradability of biopolymers, such as PLA, can be achieved. On the other hand, the addition of wood fibers enhances the material's ability to resist thermal deformation. The present compositions can be used for manufacturing hollow structures, by injection blow molding, of bottles with a wall thickness between 0.1 mm and 5 mm, in particular from 0.3 to 1 mm or continuous extruded products with a wall thickness from 0.3 mm to 1.5 mm.