We study mechanical behavior of soft rubber-like digital materials used in Polyjet multi-material 3D-printing to create deformable composite materials and flexible structures. These soft digital materials are frequently treated as linear elastic materials in the literature. However, our experiments clearly show that these materials exhibit significant non-linearities under large strain regime. Moreover, the materials demonstrate pronounced rate-dependent behavior. In particular, their instantaneous moduli as well as ultimate strain and stress significantly depend on the strain rate. To take into account both hyper- and viscoelasticity phenomena, we employ the Quasi-Linear Viscoelastic (QLV) model with instantaneous Yeoh strain-energy density function. We show that the QLV-Yeoh model accurately describes the mechanical behavior of the majority of the soft digital materials under uniaxial tension.