The objective of this work is to analyze the influence of the cross-section of a bumper beam made of fully biodegradable composites. Flax/PLA bumper beams were manufactured with four types of cross-sections with different degree of roundness. Specimens were subjected to low velocity impacts and the post-impact behavior is evaluated under three-point bending tests. Results indicate that different cross-sections can be selected if the objective is to maximize the impact performance or the post-impact residual properties. The bumper beam with the higher roundness exhibits the best impact performance, while an intermediate section exhibits the best after impact residual mechanical properties.