I don't know much about "treatments" for wool that make it wrinkle resistant, but I know that wool can be naturally wrinkle resistant. Typically, a wrinkle is formed when hydrogen bonds between chains in the fabric structure are broken and then reformed in the new position. In wrinkle-resistant treatments, strong covalent bonds replace weaker hydrogen bonds, giving the molecules more stability in their positions. So molecules are pulled back into alignement, preventing the formation of wrinkles (and no, this isn't my brilliance talking; this is from Understanding Textiles by Collier and Tortora. Resin treatments to fabric are "cured" at a high heat to create a chemical reaction that takes place with the fabric. They're not permanent, but the heat from the dryer can actually "re-energize" the resin treatment for a while. As for wool fibers, they are of course naturally elastic, and return to their crimped shape, which is why wool trousers can be "hung out" and look smooth the next day. If wool yarns are spun, twisted, and woven even tighter, the resilience goes up, and so does the wrinkle recovery. The opposite of worsted (highly twisted) wool is "woolen," which is wool left in a more natural state, more relaxed, such as Shetland and Harris Tweed type wools. Someone with more experience than I will have to correct anything I may have gotten wrong here, but I think that's basically how it works.