Not Actually Bubble Wrap
While it may look a lot like bubble wrap, the product used to cover a swimming pool and potentially heat the water is actually a solar pool cover. It looks very similar to bubble wrap, as it contains air bubbles, although the material is much thicker, sometimes as much as 12mm in thickness. The bubble wrap material is usually black in color and is the side that sits on the water while the smooth side is the side that is usually visible. These solar pool blankets are a nice, cheap way to heat a swimming pool without having to pay high gas or electricity bills. Costing around $40, these solar pool covers can be bought in sheets which you can then cut to fit the size of your pool. They work to heat your pool in two ways, by using absorbing heat from the sun's rays and by preventing heat loss.
The solar pool cover, as the name suggests, works by absorbing the sun's rays. The pool water then becomes heated through an exchange of heat. When the "bubble wrap" pool cover absorbs the suns rays it gradually heats the water in the pool while the cool pool water keeps the solar cover cool. The pool cover will usually heat the pool water up by one degree per day. After several days in full sun a pool cover can raise the pool temperature by about 10 to 15 degrees.
However, the pool needs to be under full sun for this to occur. If a swimming pool doesn't get full sun, it is unlikely that the pool owner will experience the heating effects of a solar pool cover. Most pool covers are either blue or clear. Some pool suppliers sell black pool covers claiming that it absorbs more heat. However, while it's true that darker colors absorb more heat, they also trap more heat so the heat doesn't transfer to the pool water. Additionally, because the black covers trap more heat within the cover, the covers become more prone to damage than the clear covers.
Prevents Heat Loss
The solar pool cover works in another way by preventing heat loss. At night, as the water cools, it loses radiant heat and also evaporates. However, a solar pool cover works like a blanket, keeping the heat in and preventing it from escaping. This is due to both the bubbles and the thickness of the solar cover which helps to insulate against radiant heat loss and provides a physical barrier against evaporation, meaning that not only will a solar pool cover keep a pool warm but can also help to save on water bills.