There are a few different types of pipe that can be used for outdoor faucets, but the most common is PVC. PVC is a durable material that can withstand harsh weather conditions and won't corrode like some other metals. It's also relatively easy to install, so it's a good option for do-it-yourselfers. If you're not sure which type of pipe to use for your outdoor faucet, consult a plumber or home improvement expert.