Thermoplastic composite materials can be molded into complex curvature shapes via thermoforming, where the material is heated to a pliable temperature and then formed into the desired configuration. For instance, a hemispherical composite part can be thermoformed by punching a male hemispherical tool into a flat stack of heated Ultra-High-Molecular-Weight Polyethylene (UHMWPE) composite sheets held in place by a binder ring. The quality of the as-manufactured part is dependent on many variables, including the in-plane shear constitutive response of the material, as it will dictate how easily the material conforms to the prescribed shape. Experimentally investigating the optimal set of processing parameters to achieve a hemispherical part with minimal wrinkling is time consuming and costly. Our goal is to create a computational model that can accurately simulate the thermoforming process and predict the end product quality. This will allow for rapid evaluation of optimal process parameter combinations, greatly reducing experimentation time and cost. In-plane shear characterization of DSM Dyneema HB 210 is performed at relevant process temperatures, fiber rotational rates, and preprocessing states to provide constitutive material response input for the computational process model. Biased extension tests show that an elevated temperature leads to an increase of the in-plane shear compliance. Rate effects are more pronounced at a lower temperature. Fiber rotation is upwards of plus or minus 35 deg for all specimens. LS-DYNA finite element simulations, using select in-plane shear response inputs, demonstrate the effect of the in-plane shear response on the thermoforming process, the as-manufactured part thickness, and in-plane shear distributions.