Solar cover or winter cover: they are not the same product

Two products, two entirely different jobs

They are sold in the same aisle, they are both large sheets of material shaped like your pool, and the similarity ends there. A solar cover is bubble sheet that floats directly on the water surface. A winter cover is woven polyethylene that sits over the whole pool and is secured against wind for months at a time. They are made of different materials, they are fitted differently, and they fail in different ways.

What the solar cover is actually doing

Two things at once, and both of them are about the surface. It stops evaporation while it is on, which matters twice: evaporation is the largest route by which a pool loses heat, and it is also the largest route by which it loses water. Then it lets sunlight through to the water beneath, so the pool keeps gaining heat while covered.

The practical requirements are the ones people get wrong. Bubbles face down, toward the water — the most common installation mistake in the category. Buy oversize and trim to your pool, because these are sold to be cut. And buy a reel with it, because a wet cover wrestled off by hand twice a day stops being used within a month, at which point it is heating nothing. Our solar cover roundup covers thickness and fit, and extending the season covers what it does for temperature.

What the winter cover is actually doing

Keeping the pool closed. Through the off-season a covered pool has no light reaching it, so algae cannot photosynthesize, and no leaves landing in it, so there is nothing to decompose into next spring’s problem. That is the entire job, and it is the difference between an opening that takes a morning and one that takes a fortnight.

The specification that matters is overlap. A winter cover has to extend genuinely past the wall so it can be secured all the way round, and the stated size needs checking against your actual pool rather than against the nominal diameter. Then it is secured — cable and winch, or wraparound straps — because an unsecured cover in a winter gale is gone, and it takes some of your pool with it. Our winter cover roundup covers construction and securing.

On a pool that stays up, the cover works with an air pillow rather than alone. The pillow sits centered under the cover and absorbs ice expansion, moving the load away from the wall. Inflate it to roughly 60 percent — a fully inflated pillow bursts. Our winterizing guide has the full sequence.

Why swapping them fails

Solar cover used as a winter cover. Bubble sheet is thin, it is not made to be secured, and it is not made to carry the weight of wet leaves, snow or standing water. Left on through winter it tears, and you spend spring fishing pieces of it out of the pool.

Winter cover used as a solar cover. It blocks the light, which is exactly the opposite of what you want in July, and it is far too heavy to take on and off daily. It also does not float, so it does not sit against the surface where evaporation happens.

You will genuinely use both on most pools, at different times of year. If the budget only stretches to one this season, buy the solar cover first: it earns its money every week of the summer, whereas the winter cover earns its money once, at the end.

The buying order that makes sense

Solar cover and reel in the spring, sized to your pool and cut to fit. Winter cover and, if the pool stays up, an air pillow in the autumn, checked for genuine overlap before you need them. Both are inexpensive relative to what they protect, and both are frequently missing from pool kits — check what is actually in the box before assuming you have either. Our kit versus separate guide covers what kits typically omit.