Cheap Ugg Boots are made of sheepskin, with wool inside. This makes them warm, comfortable, and tricky to clean. But they are cleanable.
Take care of your uggs. Don’t get them wet, or walk through mud. They were designed primarily as indoor footwear, so they are not as resilient to dirt as sneakers or leather boots.

When you first buy your uggs, think about buying a waterproofing spray, and a stain-repellent spray. These are typically available at shoe stores, and a sales associate will be able to provide you with some. These sprays will keep your uggs cleaner for a longer amount of time, prolonging their life.
After spraying, let the boots dry for 24 hours. Ugg Australia recommends reapplying the waterproofing frequently during the winter.

