A prepreg composite material that includes a fiber layer and a resin comprising a thermoset resin component, a curing agent and a fibrous micropulp. The micropulp component is an aramid fiber having a volume average length of from 0.01 to 100 micrometers. The prepreg is useful in composite panel construction for minimizing fluid permeation into the cured structure. This prepreg is particularly suitable for making honeycomb sandwich panels. Film adhesives, liquid and paste resins containing aramid fiber micropulp are also disclosed.