First up are pipe sizes. Pipe size can do a number of things to your project, depending upon your needs. The smaller you go, the more flexible your pipe will be. So if you need curved surfaces for a frame, need hoops or loops, go small. If you want stiffness and strength to the max, go big. As the pipes increase in size, so does their inner wall, making them stronger and more inflexible.
I’m only covering basic, white PVC available in most home stores, as ABS is too brittle (and weak) and PEX is just not as friendly.
I’ve broken down the sizes into categories below:
1/2”: Super-uber flexible, but not very strong. It can actually kink when bent. This works well for kites and other light structures, but not so much for something you want to mount anything to. Plus, it’s so small you would need tiny screws to attach anything to it.
3/4”: Very bendable, ideal for just about any project that requires flexibility, specifically hoop houses, green houses, pet agility hoops and other curved frames. This is also good if you need elasticity in your project, as it will spring back perfectly (be careful though!).
1”: Only slightly flexible, but still fairly rigid. This is if you want a bit of sway to your project, but still need a strong framework, 1” is good. Marshmallows fit in them nice and snug.
1-1/4”: This is probably the most ideal size for very rigid, lightweight project. This is perfect for framing, structure, and anything else you might need to build a strong sturdy platform, shelf, table or wall with. It still has SOME flexibility, but not much.
1-1/2”: Pretty much rigid as it gets, except for 2” (below). It’s heavy though.
2”: Probably as strong as you could ever need, will hold tons of weight. It is very heavy and very expensive in relation to other just as strong sizes. However if your project is requiring a good foundation, 2” is perfect. It also works well for canister-style projects (in conjunction with end caps), like garbage bag holders, etc.
Summary: For most projects, either 3/4” or 1-1/4” are ideal. If you need flexibility, go 3/4”, for rigidity, go 1-1/4”.