Glass sliding doors: aluminum or PVC for a patio?

Aluminum is almost always the best choice for sliding glass patio doors, and I'm telling you that because it holds up to everything you throw at it without warping. It's more resistant to temperature changes, it doesn't expand and contract like PVC does, so your door will keep sliding smoothly five years down the line. Aluminum is also more durable, it doesn't yellow in the sun, and even though it costs more upfront, it pays for itself in the long run. If your patio gets a lot of direct sun or there are pretty significant temperature swings between day and night, aluminum is definitely your friend.

PVC has its place, though. It's cheaper and works fine in mild, stable climates, but in patios with heavy sun exposure or in places where it gets really hot and really cold, you end up with problems. The glass stays the same either way (use tempered or safety glass, no question), but the frame is what makes the difference. With aluminum you also get less maintenance - you don't need to constantly clean joints or worry about seals degrading.

If your budget is really tight and your patio is protected (under an eave or without constant sun), PVC works. But if you want a door that holds up year after year with no headaches, aluminum is worth the extra investment.