Refresh your UnderCool 3 with a new set of ThermApparel SlimCool cooling packs designed for comfort, discretion, and all-day wear.

These lightweight PCM SlimCool cooling packs freeze and melt at 70°F (21°C).

Think of it like a heat exchanger: the packs pull heat out of the blood flowing through vessels near your skin, and your body circulates that cooled blood back through your entire system, bringing your core temperature down from the inside out.

They recharge quickly and provide dry, gentle cooling that won't shock your skin or soak your clothes, perfect for wheelchair users and anyone wearing tight-fitting costumes, uniforms, or layered outfits.

They don't sweat or condensate, so your clothing, wheelchair, and gear stay dry and comfortable.

Key Features

• Replacement cooling packs for ThermApparel UnderCool 3 (SlimCool configuration)
• Freezes and melts at 70°F (21°C) for comfortable, gentle cooling (not ice-cold)
• Ultra-slim, low-bulk design ideal for wheelchairs, tight-fitting costumes, uniforms, or wearing under everyday clothing
• No sweating or condensation, so your skin, clothing, wheelchair, and costumes stay dry
• Works in both humid and dry heat for reliable cooling at home, work, conventions, and outdoor events
• Fast refreeze times: 30 minutes in ice water, 45 minutes in the freezer, or 60 minutes in the fridge
• Non-toxic, bio-based PCM that is biodegradable and reusable thousands of times

Learn more about how our cooling packs work in our cooling pack guide.