Why are solar covers for pools blue shiny and smooth if the idea is to absorb the heat not reflect it?

The solar blanket is designed to retain thermal energy not to collect it. Covering the pool at night will help trap heat gain. I'm sure the colour is not important other than for looks.

The air in the bubbles of the cover is heated by the sun and in turn that heat energy is transfered to the pool water. You will note when first getting into a pool that has just had the cover removed that only the first two feet or so are actually heated. The continued circulation by the pump completes the cycle of moving that heated water and blending it with the cooler.

Of the ten to 15 degrees you gain in the day time -- you loose possibly 5 - 8 degrees overnight. The bubble cover does not retain heat well since the reverse happens at night cooling the water some.

k