The mechanical behavior of thermoplastics in monotonic loading is characterized by an initial linear elastic response, followed by distributed yielding, large-scale plastic flow, and gradual strain stiffening until failure is initiated. In this study we have experimentally and theoretically studied the deformation behavior of ultra high molecular weight polyethylene (UHMWPE). The goal of the study was to compare the predictive capabilities of a new constitutive theory for thermoplastics with predictions from traditional models such as J2-plasticity and linear viscoelasticity. The results from the study indicate that the new constitutive model outperforms the traditional and commonly used models, demonstrating that with an appropriate choice of material model it is possible to perform accurate finite element simulations of thermoplastic components.