4 basic types: 1) anything not bike specific. This includes jeans, skiwear, ppe type stuff and mankinis. To be avoided as they don't offer any abrasive protection. The only exception is waterproof over trousers providing you wear proper biking trousers underneath. 2) leather - with or without tassels. Traditional and can be good. Watch out for buffalo, and other animal skins which are not cow hide. Also look for the thickness of the leather, knee/hip protection and stitching as the quality of these varies tremendously. Not waterproof, cold, and can be quite gay (some people might say). Good quality with knee and hips inserts are probably the best protection you can get. Horrible to put on wet or on a hot day when your legs are sweaty. 3) textile including goretex and cordura. Mainly waterproof, for a while anyway but will end up leaking around the crutch at some point. High end gives good protection and normally a zip in liner for cold days. More give than leather and most have the ability to incorporate knee and hip pads. 4 Kevlar jeans. Again, quality counts. Varying degrees of quality coverage of the actual Kevlar. Not waterproof but better if you are walking or not riding for all of the day. Not as many funny looks from non bikers, especially compared to wearing too tight leather tassel trousers or an all in one power ranger come leather onesie race suit. Personally cordura for most of the time and Kevlar jeans for camping or summer day riding. Hood for jeans and RST for cordura would be a good start for me. Always with body armour inserts. Lots of very cheap Asian stuff about which is dubious quality. It doesn't matter how thick the item is if it isn't properly stitched with the correct thread. It will just come apart at the seams.