Here are some of the most popular cat tree and condo materials:
Sisal Rope - Extremely hard wearing and durable, sisal rope is the best choice for scratching posts and climbing. Your indoor cats will be able to use it to keep their claws down as well as enjoying climbing up to higher platforms.
Carpet
Soft yet claw resistant, carpet is a popular choice for covering cat tree frames. Your cat's claws can sink into it, and they can use it to climb up the different levels. Less durable than sisal, carpet is more comfortable for perches and lounging platforms. Just don't expect it to last forever, though.
Polyester
If you opt for a hanging cat tree, you may want to look for a machine washable polyester version. Simply unhook it and stick it in your machine for hassle-free maintenance.
Polyester hanging cat trees also make comfortable beds for your cats, and it is a highly resistant material that should stand up to their claws. However, you should expect some deterioration in looks with use over time.
Wooden frame
A lot of cat trees feature wooden frames. Some are exposed, while others are covered in sisal and carpet. Exposed wooden areas of the  frame can improve the appearance of your cat tree and they are also easy to dust and wipe clean, unlike the carpeted versions that will need to be regularly hoovered.