What side goes where on a solar pool cover?

Solar pool covers should generally face bubble side down. Solar covers feature a sturdy construction with polymer material, which contains up to thousands of very small sealed air bubbles, and floats with the bubble side down when the pool is not in use.

Having the pool cover float with the bubble side down ensures that the bubbles help to trap the sun's rays, which heats the bubbles and ensures that the water below the bubbles gets heated. When the pool cover has the bubbles facing down instead of up, it makes for much faster transfer of heat since the bubbles are in direct contact with the water.