Technically, all you really need to cover the pool is a large sheet of plastic. Plastics meet the requirements to become a vapor barrier.
But a large sheet of plastic you get from the woodshop is probably not your best option. It will be very difficult to handle and store, it tears easily, and sunlight will deteriorate rapidly. If you’re looking for solar pool cover reel system, you can browse various online sources.
You can use a piece of plastic, but it would be very inconvenient and probably will only last 1 to 2 seasons maximum.
It’s best to use a specially designed cover for the pool. They are made of special materials, such as UV-stabilized polyethylene, polypropylene, or vinyl. They can be transparent or opaque. Covers can even be light or dark in color.
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One of the lowest costs of quilts made specifically for the pool is a bubble (or solar) cover. The wraparound bubble was similar to the bubble packing material unless they use a thicker grade of plastic and has a UV inhibitor.
Vinyl cover consists of a heavier material and has a longer life expectancy than bubble covers. Isolated vinyl cover is also available with a thin layer of flexible insulation sandwiched between two layers of vinyl.
An outdoor pool heat gains from the sun, absorbing 75% -85% of the solar energy striking the surface of the pond.
This is an important contribution to this pool heating needs. A swimming pool cover will reduce solar gain contribution to some extent, depending on what type you are using.
A transparent bubble cover can reduce the absorption of the solar energy pool by 5% -15%. A totally opaque cover will reduce by 20% -40%. You need to consider this when choosing a swimming pool cover.