Why UGG Boots Keep You Warm: Sheepskin, Sizing, and Which UGG to Buy

Quick answer: UGG boots keep you warm because genuine twinface sheepskin traps heat while letting moisture escape, so your feet stay cozy without getting as sweaty as they would in many synthetic linings. For sizing, the sheepskin packs down and molds to your foot, so UGG boots should feel snug at first. If you're a half size, UGG suggests going down to the nearest whole size in classic styles.

Twinface sheepskin is one piece of material: soft suede on the outside and natural wool on the inside. Wool fibers trap air, which holds in warmth, and they also help pull moisture away from your skin. That's why UGGs feel warm on a cold day but don't turn into a sauna indoors.

Wool is one of nature's best insulators. Each fiber is crimped (wavy), so it creates lots of tiny air pockets. Those pockets hold your body heat close to your foot.

Wool can also soak up some moisture without feeling wet, and the suede side lets air pass through. So when your feet warm up, sweat has somewhere to go. In many boots with synthetic linings, sweat gets trapped, your feet feel damp, and then they get cold. Sheepskin helps keep that from happening.

UGG classics were designed to be worn barefoot. Here's what that means for comfort and fit.

JD Expert Question: "Should I wear socks with UGG boots, and will the sheepskin flatten over time?"

JD Expert Answer: Going barefoot lets the wool do its job and gives you the softest feel. Socks are fine too. Thin, breathable socks (like wool or cotton) work best, while thick synthetic socks can trap sweat and make your feet feel warmer and damper. The sheepskin will pack down and mold to your foot over the first few weeks. That's normal, and it's why UGGs should feel snug, not loose, when they're new.

• Warmth and comfort:

• UGG twinface sheepskin: Holds warmth and breathes, so your feet are less likely to overheat.

• Faux fur: Can feel warm at first but often traps sweat, which can lead to damp feet and odor.

• How it holds up:

• UGG twinface sheepskin: The suede and wool are one piece, so the lining can't peel away from the boot.

• Faux fur: Glued-in linings can bunch up or come loose over time, especially at the heel.

• Snug at first: New UGGs should feel snug. The sheepskin packs down and molds to your foot, so a loose pair will feel even looser later.
• Half sizes: If you're a half size, UGG suggests going down to the nearest whole size in classic sheepskin boots.
• Socks or barefoot: Try them on the way you plan to wear them. If you always wear thick socks, stay at your true size.
• Slippers and sneakers: Styles like the Tasman and Lowmel can fit differently, so check the size guide for each style.

• Classic Short or Classic Mini: The iconic look with more ankle coverage. Best for cold, dry days.
• Classic Ultra Mini: The low-cut favorite. Easy to slip on and great with leggings or joggers.
• Tasman: A slipper you can wear outside, with a sturdy sole. Great for errands and around the house.
• Lowmel: A sneaker-style UGG with a cozy lining for people who want sneaker shape with UGG comfort.
• For snow and slush: Classic sheepskin isn't waterproof. Treat it with a suede protector, or pick a weather-ready UGG style.

• Are UGG boots still popular for winter? Yes. The Classic Ultra Mini and Tasman are some of the most popular winter styles.
• Do UGGs run big? They run a little big as the sheepskin packs down. If you're a half size, go down.
• Are UGG boots waterproof? Classic sheepskin UGGs aren't. Use a suede protector spray and avoid deep snow or slush.
• Can you wear UGGs without socks? Yes. They were designed to be worn barefoot.

Who should buy UGG for the sheepskin?

UGG is for anyone who wants real warmth and soft comfort for cold days, lazy weekends, and recovery after a workout. Genuine sheepskin keeps you cozy without trapping sweat, and it molds to your foot over time.

• Buy the Classic Ultra Mini if: You want the most popular easy-wear UGG for fall and winter.
• Buy the Tasman if: You want a slipper you can also wear out.
• Ready to shop? Browse the latest UGG at JD Sports.

• UGG Product Information: Details on twinface sheepskin, UGGpure™ wool, and Treadlite by UGG™ outsoles.
• UGG Sizing Guide: Fit advice for classic boots, slippers, and sneakers.
• Material Basics: General information on how wool insulates and handles moisture.
• JD Sports Fit Feedback: Sizing and comfort feedback from JD Sports store teams across North America.