There seem to be a lot of questions about the purpose of an air pillow in this forum. The main reason for a pillow is for "ice compensation" on TOP of the cover. Many people think it's for the pool water, but it's not. The water, ice and snow accumulate on top of the cover, and if there is no pillow, the weight and pressure push out like a glacier towards the sides of the pool. Since the pool water is lower, there is a gap under the cover between the edge of the pool and where the cover reaches the top of the water, and the ice and snow push out, putting pressure on the cover and side walls. With an air pillow in the middle of the pool under the cover, the ice and snow can press in, compressing the air pillow and alleviate some of the pressure on the cover and pool walls. An added benefit is water and debris management in the spring. Having a pillow in the center sheds the water and leaves to the sides of the pool making it easier to clean and pump off. To help install the pillow and to keep it centered people in this forum have talked about using The Pool Pillow Pal.