Low sintering leaves PTFE unmelted, causing micro-pores, poor adhesion, rough surfaces, low mechanical strength, and milky appearance. Overheating degrades PTFE, producing pinholes, bubbles, brittleness, yellow-to-black color, and toxic fumes. Both ruin compactness, non-stick performance, flexibility, insulation, and dimensional stability. Optimal range 370–400°C yields semi-transparent, smooth, tan coating. Visual check: matte white = under-sintered; yellow/brittle = over-sintered. (296 chars)