Foam extrusion experiments were performed to study the effects of surrounding temperature variation on cell structure and foam density. Linear low density polyethylene and low density polyethylene were used with an endothermic chemical blowing agent in a single screw extruder with a capillary die to form foam rod samples at different surrounding temperatures. Cell density, foam density, and cell morphology were investigated. Although surrounding temperature thermally affects the outer thin skin layer, the overall structure is obviously affected. Skin formation, foaming, and melt capability to sustain the cells are discussed in this article.