Heat Retention: Solar hot tub cover with thousands of thermal bubbles can trap the heat and keep the water warm. For outdoor use, it can absorb sun energy to heat up to reduce heating time.12 mil is thicker to achieve a great heat retention. Reduce Spa Cost Eficiently: Not only the hot tub blanket can reduce cost in energy of heating up, but also in water evaporation. Prevent water evaporation by 95%. Enjoy your spa time without worrying too much cost on energy or water. Trim to Fit: Suitable for inground or above-ground pool.