Effects of the properties of polymers and blowing liquids on the macrostructure and microstructure of foamed products in a dynamic decompression and cooling (DDC) process have been investigated. When the homogeneous solutions, prepared by the heating and mixing of the mixtures of low-density polyethylenes (LDPE) and chlorinated hydrocarbons under nitrogen (Nz), go through a rapid pressure quench above the boiling point of the liquids, bubbles nucleate out through liquid/gas phase separation and grow through diffusion and expansion of the gaseous phases. Foam cell stabilization is improved by polymers exhibiting higher extensional hardening and blowing liquids possessing higher latent heat of evaporation. Resultant LDPE foams have mixed cell structures: in the skin parts, more cells are closed, but more cells are open in the core parts. In the polymer matrix, micromorphologies of granules, fibers, and fiber networks, with oriented lamellae, are observed. The formation of these complex structures is described in terms of phase and deformation behaviors of the solutions.