A solar pool cover is one of those purchases that seems simple until you realize there are several ways to get it wrong. The Shop Square 18 Foot Round Solar Cover for Inground and Above Ground Pools, 12 Mil is designed to do three things: warm your water, cut down on evaporation, and keep leaves and dirt out. But before you buy, you need to know whether this particular cover is the right fit for your pool and whether solar covers make sense for you at all.

What Does an 18 Foot Round Solar Cover Actually Do?

A solar pool cover works by absorbing sunlight during the day and trapping that heat in your pool water at night. The Shop Square model uses bubbles facing downward against the water surface to maximize heat transfer. Because the cover sits on top of your pool, it also prevents water from evaporating into the air—a benefit that matters more in dry climates or during hot months. The added bonus is that leaves, dirt, and debris can't fall into your water.

The trade-off is that you have to put the cover on and take it off regularly. Some people find this an easy routine; others see it as a chore. Think honestly about your habits before buying.

Figuring Out If 18 Feet Is Your Size

The critical step here is measuring your pool. An 18 foot round solar cover is designed for pools with an 18 foot diameter. If your pool is smaller, the cover won't fit snugly and won't work as intended. If your pool is larger, you won't be able to cover the whole surface.

Grab a tape measure and run it across the widest part of your pool, going through the center. That's your diameter. If you have an above ground pool, check the original packaging or your purchase paperwork—manufacturers always label the size clearly. For inground pools, you may need to measure or recall what size you had installed.

The Shop Square 18 Foot Round Solar Cover works for both inground and above ground pools of that size. The design includes trim lines and marked bubbles so you can customize the fit slightly if needed, using a marker and sharp scissors, but these adjustments are minor. They're not meant to resize a cover that's the wrong size to begin with.

Understanding the 12 Mil Thickness

Mil is a unit of thickness—one mil equals one-thousandth of an inch. At 12 mil, the Shop Square solar blanket for above ground pool sits in the heavy-duty range. A thicker cover lasts longer, resists tears and punctures, and doesn't degrade as quickly under UV exposure. The tradeoff is that heavier covers can be slightly more awkward to handle when you're pulling them off or folding them for storage, though 12 mil is still considered manageable by most pool owners. Thinner covers are cheaper but need replacing more often.

Caring for Your Solar Cover and Knowing When to Replace It

A solar cover isn't permanent. Over time, UV rays break down the plastic and the bubbles can flatten or separate. How long yours lasts depends on how much direct sun it gets, how you store it, and how carefully you handle it. Many owners get several seasons out of a 12 mil cover if they store it indoors during winter and keep it clean.

When you're not using your cover, rinse off any leaves or dirt, let it dry completely, and store it in a cool, dark place—not crumpled in direct sunlight. Avoid sharp objects and rough surfaces that can puncture it. If you notice tears, holes, or areas where bubbles have separated, the cover's efficiency drops. Eventually, replacement becomes the better choice than repair.

Is a Solar Cover Right for You?

A solar pool cover makes the most sense if you want to extend your swimming season or reduce heating costs over the long term. It's less useful if you only swim occasionally, live in a very cloudy climate, or hate managing another piece of equipment. The Shop Square 18 Foot Round Solar Cover for Inground and Above Ground Pools, 12 Mil is a straightforward option if your pool diameter matches and the effort feels manageable to you.

The product in this guide: 18 Foot Round Solar Cover for Inground and Above Ground Pools, 12 Mil - Premium Heavy Duty Solar Blanket for Above Ground Pool, Blue - Made in USA