Now that Spring is finally here, we can start hoping for a really nice day and jumping into the swimming pool again – but how can you heat it up in a way that’s not going to cost a fortune and might even be greener than cranking the heater for hours? The answer lies inside our favorite plastic circles. Make Magazine writes, “Here’s an easy way to warm your pool that’s efficient, low-cost, safe, and actually enhances the beauty of the pool. The Lily Pad pool warmer doesn’t need to be removed to swim, sweep, or vacuum, and it meets new requirements in water conservation areas to keep at least half of a pool’s surface covered.” You can make your own Lily Pad pool warmers by repurposing a hula hoop and stretching black polyethylene film (black plastic tarp) over it. They’ve soldered the tarp to the hoop itself, although you may be able to come up with other ideas on how to make the relatively simple idea work. Make says, “The film is in contact with the water, so it captures and transmits most of the sun’s incoming radiation directly into the pool, warming the surface of the water. Calorimetric tests have shown that at high noon, a single Lily Pad will transmit more than 500 BTU per hour.” We think they look a lot cuter too – and you don’t have to remove them all to be able to use, or even clean the pool either.