In the case of the coPBS_20%nHAp sample, its values decrease by up to 50%, while for the coPBS_20%µHAp sample it decreases by about 30%. The reason should be sought in the much higher value of specific surface area in the case of nHAp particles. Their interaction with the polymer matrix is much greater than in the case of HAp whiskers. Thus, for materials containing nHAp, the flow of the material in the plastic state is hindered, which may result in poorer processing properties.