Universal crib conversion rails can be made of solid wood, MDF, plywood, plastic and metal. Metal and solid wood tower above the rest when it comes to durability, stability and aesthetics. Metal works best if you are looking to add a protective mesh screen to the rail.
Oak, maple, cherry wood, cedar and pine are some of the local varieties of wood used for making rails whereas rubber wood is a sustainable variety that is now used globally for making furniture.
These can be finished and stained in hundreds of ways to match the décor and they last for years with minimum upkeep. But they usually cost high upfront and if you aren’t looking to spend that kind of money, then plywood or MDF offers a safe middle ground. It’s not as durable as wood or metal. But it isn’t as flimsy as plastic either.