PEX-A (Engel method, highest crosslink): 3/4in. ASTM F876/F877. Advantages over copper: flexible (fewer fittings = fewer leak points), freeze-resistant (expands without bursting), no corrosion, quiet (no water hammer), lower cost. PEX-A vs PEX-B: A is more flexible, uses expansion fittings (Uponor/Wirsbo), memory allows re-expansion if kinked. B uses crimp/clamp fittings. Manifold system: home-run from central manifold (each fixture gets dedicated line) — best water delivery, easy shut-off, more tubing. Trunk-and-branch: traditional layout, less tubing, shared pressure. Max temp: 200F. Pressure: 100 psi at 180F, 160 psi at 73F. Not UV-resistant (cover within 30 days of outdoor exposure). Support: 32in horizontal, every floor vertical. Color: red (hot), blue (cold), white (either). Cost: $0.75-$1.50/lf. CSI 22 11 13.