Composite materials developed in this study were produced from a mixture of shellac resin as matrix, reinforced with cellulose. The influence of the reinforcement content, as well as, the concentration of additives on mechanical performance and the facility to process were studied. As a result wide range of mechanical properties were obtained: (i) high content of cellulose, but low concentration of ethanol and polyethylene glycol provided biocomposite with high stress resistance and Young’s modulus, (ii) lower content of cellulose, but high concentration of additives gave samples with low Young’s modulus and high elasticity. Two cellulose-based reinforcements with different polarity, namely mechanically refined wood pulp and cellulose acetate butyrate particles were thus compared. The efficiency of the composite over two model reinforcements, i.e., hydrophilic and hydrophobic component, respectively, were also studied. Although particles reinforcement was easier to process and evenly dispersed into the matrix, mechanical performance was lower compared with refined fibres. SEM images showed the matrix better coated the fibres than particles, which resulted in better adhesion and mechanical performance in the first case. The morphology of reinforcement plays a key role; long fibres oriented in the pooling direction ensure a better mechanical resistance than particle fillers.