There are three most common materials used – steel, aluminum, and wood. The steel ones are the most durable and an excellent option for the aggressive dogs. The aluminum kennels are a bit lighter but equally as durable, while the wooden ones look the best but aren’t as safe as the two previous versions. For smaller and not aggressive dogs check top soft-sided crates.
The Stationary version of the crate goes further, it is an IATA 82 dog crate which you will need if you are traveling with dogs more commonly associated as fighting or dangerous breeds. This means that that Stationary Crate’s industrial tough design meets the special enhanced IATA CR 82 dog cage requirements for for travel with pitbulls, mastiffs and other breeds that are claimed to be powerful, aggressive, fighting or dangerous.
Update: We traveled quite a bit this holiday season and this portable crate was absolutely awesome! I have seen some reviews about bad zippers but suspect it's due to misuse. You have to raise each side before zipping it -- just common sense, people. Otherwise, there is too much pressure on the zipper. I think zippers on this crate are sturdy. Another suggestion is placing your dog's favorite bed inside. The crate (we have extra large) has plenty of room to add an extra large fluffy dog bed our dog loves. Because the crate folds flat, we place the crate in the cargo area and cover it with dog's bed when on the road. The dog sprawls like a queen! :) When we get to the destination, we unfold the crate, throw the bed inside, and voila -- cozy house that ... full review