The Pool-Mate Deluxe Winterizing Air Pillow absorbs stress created by ice building up in your pool. As ice expands in your pool the pressure created is exerted onto the pillow instead of the walls of your pool. Ice equalizer pillows are an essential way to protect your pool during the winter. The pillow will pop before the ice damages your pool. Ice Equalizer pillows also reduce the build-up of rain water, leaves, and snow on your winter cover. All you have to do is inflate the pillow and place it under your cover during the winter months. Do not overfill the pillow with air, as this can cause the valve to pop out during the winter months (1/2 to 3/4 full is recommended). Smaller equalizer pillows are recommended for round pools and larger equalizer pillows are recommended for oval pools. Using additional pillows will protect your pool if 1-fails. Using additional pillows may require a larger than expected pool cover size.