Open textile structures made of AR glass filament yarns are finding increasing application in civil engineering, e.g. as reinforcement in thin concrete strengthening layers. A knowledge of material parameters is a precondition for the application of such materials. In this paper, experimental and numerical investigations aimed at collecting information on the uncertain material parameters of AR glass filament yarns are presented. This information serves as a basis for mathematical modelling. Uncertainty is here interpreted as fuzzy randomness, and quantified using fuzzy probability distribution functions.