When evaluating PVC foam pipes (also known as cellular core PVC), you must prioritize density and structural integrity. Ensure the pipe features a tri-layer construction where the inner and outer layers are solid PVC for chemical resistance, while the middle layer is foamed to reduce weight. Key metrics include Shore D hardness (typically 70-80), thermal conductivity (lower is better for insulation), and impact strength. For drainage applications, verify the pipe stiffness (PS) rating, usually categorized as PS25, PS50, or PS100.