The materials used depend on what the crating needs are. If you’re just shipping the work for a one time trip, then wood is an inexpensive option. A basic well-constructed box with internal sheet foam padding will do fine for a one-timer.
If you need the crate to last longer than a one-timer, then there are several options/materials to consider. In my opinion, wood offers the best protection for fine art shipping solutions. A well-constructed wood crate, reinforced with wood framing is a good long term, multi-use solution. Add re-closeable hardware and a long-lasting foam padding interior and you’ll have a crate that’ll last for years.
Another option would be to make what’s called a slat crate. It’s constructed of a wood-framed, cage-like shell with side panels made of a lighter material, such as extruded plastic, 1/4" fiberboard, etc.. This is a good option if you want to keep the weight on the light side. There are times when a slat crate can be used with no protective sides, just a framed wood cage. This option is good when using fine art handling installation services for shipping (door to door, critical care). It only offers some protection while keeping the focus on other aspects, like maintaining the shipped art in a specific position during transit, for example.
These are just a few basic options for crating. There are many more things to consider that I can’t get into for the sake of keeping it short. A good site to visit for fine art packing crating services information is Activity Stream
Shipping options and costs are a big factor when considering how to create art. If wanting to keep fine art moving shipping costs down, the lighter and smaller the better. But please don’t sacrifice the protection of the shipped object for the fine art storage warehousing the costs down. You’ll end up paying way more in the long run with damaged goods.