AbstractThe effect of fiber geometry on the fracture behavior of short glass fiber‐reinforced nylons was examined. In particular a comparison was made between conventional short‐fiber composites (with feedstock made by an extrusion process) and the newer pultruded feedstock materials which have longer fiber length distributions but larger fiber diameters. The toughness of the material was measured over a wide range of loading rates, from impact conditions, using Kc and Gc type tests, to long term, slow crack growth tests. The moisture content of the materials was varied from dry to saturated. It was found that there was little difference in fracture toughness when the materials were dry. However, when moist, the longer fiber material showed significant improvements over the conventional short‐fiber‐reinforced material. This behavior is explained in terms of the changes in fiber geometry.