Solar Covers - Good or Bad to Double Them?


Platinum Supporter
LifeTime Supporter
Jun 28, 2009
I have a 12 mil clear solar cover and also a light blue 8 mil.

I have been keeping the clear one on during the day and then when the sun goes down I put the light blue one on top of the clear one. My theory is that by putting the second one on I am trapping more heat inside the pool. My water is barely 80 and I like it almost 90, so the quicker the better for getting it warmed up.

1. Does anyone know if putting on the second cover at night is a good plan?
2. If I were to keep both covers on during sunlight hours, would I get a warmer pool faster? Or would the the top cover somehow magnify the heat on the bottom cover and ruin the bottom cover and/or prevent the pool from getting as warm as it would with only one solar cover? Or none of the above?

Thanks for any input.


LifeTime Supporter
Jan 11, 2009
Cupertino, CA
The main function of a solar cover is to reduce evaporation (because evaporation cools the remaining water). Doubling the cover won't affect that, it would only affect conduction/radiation through the cover. I don't know as anybody has tried to measure that, but I'd expect it to be a minor effect.

The solar cover marketers try to make a big thing about focusing the sun's rays to increase the heating power, which is all nonsense. The total solar energy falling on the pool's surface area doesn't change, therefore the heating effect can't be increased that way. Plus, the solar cover bubbles are not proper lenses. There is no focusing effect.

Conventional wisdom is that having the cover off during the day warms the water the most; having a clear cover on is second best. This is because more of the sun's energy reaches the water through radiation, rather than the cover absorbing it and either reradiating or convecting the energy into the water. So, I think doubling the cover during the day would be counter-productive.