TPO: thermoplastic polyolefin, 60 mil thickness. White surface reflects solar radiation (Energy Star, Cool Roof Rating Council listed). SRI (Solar Reflectance Index) >80. ASTM D6878. Installation: mechanically attached or fully adhered. Seams: hot-air welded (automatic or hand welder) — strongest seam in single-ply roofing. Sheet width: 6, 8, 10, or 12 ft. Flashing: pre-fabricated TPO accessories (inside/outside corners, pipe boots, drain sumps). Min slope: 1/4 in/ft recommended. Cost: $4-$8/sf installed. Lifespan: 20-30 years. Advantages: energy savings (cool roof), weldable seams (stronger than adhesive), chemical resistant, recyclable. Disadvantages: formulation variations between manufacturers, requires skilled welder for seams, newer track record than EPDM. CSI 07 54 23.