Ugg boots are made from sheepskins with fleece attached. The fleece is tanned into the leather and the boot is assembled with the fleece on the inside. The soles of the boots are commonly made from Ethylene-vinyl acetate (or EVA), and the stitching is often prominent on the outside of the boot. The fleece draws away moisture, keeping the feet dry and at body temperature. The original design was a pull-on boot in natural (undyed) tan sheepskin, about 10 inches (25 cm) in height, with rounded, almost shapeless uppers; this is now described as the "classic" design. Today they come in a variety of colours, including black, pink, blue, chestnut, and fuchsia. They are available in both pull-on and lace-up varieties and their height can range from just above the ankle to above the knee. Ugg boots often have a synthetic sole, although this is not universal. They are available in a range of different colours, and they are produced by a number of manufacturers. The natural insulative properties of sheepskin gives thermostatic properties to the boots: the thick fleecy fibers on the inner part of the boots wick moisture and allow air to circulate, keeping the feet at body temperature. Ugg boots are able to keep feet warm in relatively cold weather even if they are worn without socks.

Some variations of ugg style boots have also been made from kangaroo fur and leather. There are also synthetic boots. Although derided as "fake" by some in the industry, their lower price made them appealing to large retail chains such as Myer. In 2009 American podiatrist Ed Chairman raised concern that the regular wearing of ugg boots could be deleterious to foot health due to the lack of arch support.