Six different fibers were sampled from industrial wood mills in the province of Quebec in eastern Canada: Trembling aspen wood, black spruce wood, white birch wood, trembling aspen bark, black spruce bark, and bleached cellulose pulp. Wood and bark are particle type reinforcements while cellulose pulp is a fiber type reinforcement. In the present study, the word fiber is used for all types of reinforcement. Prior to composite processing, fibers were air-dried to a moisture content of about 10% (dry basis). Fibers were milled with a Wiley Laboratory Mill Model 4 and sieved with a Ro-Tap Laboratory Sieve Shaker. Milling and sieving parameters were optimized to obtain similar lengths and length distributions among the six fibers (Table 1 and Fig. 2). For particle type reinforcements, the mill was mounted with a 2-mm opening sieve and the 150–710 μm opening fraction (100 to 25 US mesh) was kept from the sieve shaker. For the fiber type reinforcement, the mill was mounted with a 1-mm opening sieve and fibers were milled three times. This procedure allowed reducing the fiber length toward the length of the particle reinforcements. The sieving process was unsuccessful for the pulp fibers as they agglomerate together, forming fiber balls. Finally, fibers were oven-dried at 80 °C to approximately 3% moisture content.