PEX

PEX is polyethylene whose polymer chains are chemically or physically linked, making it more flexible and durable than straight polyethylene. It won't kink like copper, resists chlorine degradation better than standard poly, and handles freeze-thaw cycles without cracking—so it's standard for supply runs, especially in slabs and crawlspaces where you need bend radius and cost savings.

Installation is straightforward: crimp or push fittings, no solder, no special tools beyond a crimper or expansion tool depending on the system. Color coding (red/hot, blue/cold, white/either) keeps runs organized on job sites. PEX performs well under typical residential pressures (80 psi nominal, 100 psi burst) and holds up to 180°F continuously, which covers normal water heaters and radiant loop temps.

Key limitation: sunlight degrades PEX, so it must be protected or opaqued—you can't run it openly. Some jurisdictions and inspectors still distrust it or impose restrictions, so check local code before sizing a whole-house conversion. It's proven reliable since the 1980s in Europe and 1990s here, but it's not yet mandated everywhere. Proper support spacing (every 32 inches) and protection from UV and sharp edges prevents problems.