The Inventors modify a commercially available inkjet 3D printer to modified to simultaneously print with different solid and liquid materials. Via hydraulic pressure, a liquid material alongside a flexible material is continuously distributed with adjacent droplets of each material type. Multi-material objects fabricated in this manner are specified by an occupancy matrix. The entries of this matrix correspond to the voxels of the part that will be built. Materials with mechanical properties that differ from the base materials can be specified by assigning different fractions of randomly chosen voxels to one material type or another, assuming that the chosen voxels lie within the bounding surface of the part that will be fabricated. This approach allows customized PVMs to be designed and fabricated based on an algorithm that factors in whether the viscoelastic material is likely to be used in small or large deformations. Vibration damping applications typically fall into the former category, while impact absorbing cases fit the latter. The desired material property is chosen, and the liquid percentage is generated based on an algorithm developed by the Inventors.