Preparation and properties of composites consisting of two continuous interpenetrating phases, at least one of them is the polymer phase, are presented. Three different kinds of such composites are discussed: polymer-polymer (PVC-PMMA), polymer-mineral (PMMA-gypsum) and polymer-metal (PVC-Wood alloy). Composites were prepared by filling the porous matrix made of one component with other component in the liquid state which was then solidified by polymerization (PMMA) or cooling (Wood alloy). The obtained composites were characterized mainly by mechanical testing, e.g. elasticity modulus, flexural strength and Brinell hardness. In some cases other measurements, such as microscopic and electrical, were also carried out. It was found that obtained composites possess many interesting properties. The introduction of the second component into the matrix pores as a rule increases the mechanical properties by few times, even if its content is relatively small.