What Mil Is Best for a Solar Pool Cover?

What mil is best for solar pool cover owners depends on how you will handle the cover more than on the number alone. Makers sell bubble solar covers at 8, 12, 14, and 16 mil, and the main thing a higher number buys, on the maker pages reviewed for this guide, is a longer limited warranty. A thicker cover also means more material to pull, fold, and store. For a small above ground pool you uncover by hand most days, an 8 or 12 mil cover is the practical pick. For a large inground pool with a cover reel, 12 to 16 mil makes sense if you want the longer warranty terms. In every case, care and storage matter as much as thickness.

Safety first: no thickness turns a solar cover into a safety cover. Blue Wave’s installation and use instructions for its 12 mil solar blanket say the blanket is not a safety device, is not designed to support the weight of a person, and must be removed before swimming. A CPSC release says non-rigid covers such as solar covers do not provide protection from drowning, and that they can appear to be in place even after children slip underneath them into the water. A 1980 CPSC warning about solar pool covers urges pool owners never to leave such a cover partially in place.

What “mil” means on a solar pool cover

A mil is a unit of thickness, not a millimeter. The NIST Guide to the SI conversion table lists the mil as 0.001 inch. A 12 mil cover is 0.012 inch thick, and a 16 mil cover is 0.016 inch thick. On a bubble cover, the number describes the plastic sheet the cover is made from, so going from 8 to 16 mil doubles the thickness of that sheet, even though both covers still look thin in your hands.

Not every maker prints a mil number. Intex’s product page for its solar pool cover for 15 ft round pools lists the pool size it fits and describes the air bubbles, but it gives no thickness. If a cover you are looking at has no mil rating, you cannot compare it on this point, and you should lean on the warranty terms and the care instructions instead.

Solar pool cover thickness options makers actually sell

Two lineups show how thickness and warranty line up in practice. Blue Wave sells its own solar blankets on its website, and In The Swim sells its own line of solar covers on its site. The table lists only what those pages say. Warranty terms are the maker’s, and both makers point to the owner’s manual or warranty card for the full terms.

Maker and line	Thickness	Pool type on the page	Warranty listed
Blue Wave blue solar blanket	8 mil	Round above ground	3-year
Blue Wave blue solar blanket	12 mil	Rectangular inground	5-year
Blue Wave clear solar blanket	12 mil	Round above ground	5-year
Blue Wave clear solar blanket	14 mil	Rectangular inground	6-year
In The Swim Standard (blue)	8 mil	Inground, 16 x 32 ft rectangle	3-year
In The Swim Premium (blue)	12 mil	16 x 32 ft rectangle	5-year in the feature list (the specification block shows both 5-Year and 7-Year)
In The Swim Ultra (grey)	16 mil	Inground, 16 x 32 ft rectangle	7-year

The pattern is consistent: in both lineups, the longer warranty goes with the thicker sheet. Blue Wave’s lineup stops at 14 mil. Of the two lineups, only In The Swim lists a 16 mil cover. The 12 mil In The Swim page lists two different warranty lengths, so confirm the term on the warranty card before you count on the longer one.

What a thicker cover buys you

The clearest, sourced benefit is the warranty term. Read what that warranty covers, though, because it is narrower than the headline number suggests.

• The warranty is prorated. Blue Wave’s 8 mil warranty card has the buyer pay nothing toward a replacement in the first year, 50% of the maker’s list price in the second year, and 90% in the third. The 12 mil card linked above runs 0%, then 35%, 50%, 70%, and 90% over five years.
• It covers two defects. Both Blue Wave cards say the only things covered are delamination and seam failure. In The Swim’s 12 and 16 mil pages also name delamination and seam separation as covered.
• It excludes the common ways covers fail. In The Swim’s 8 mil page says bubble damage is not a defect and is caused by acidic water conditions or high chlorine, and it excludes sun damage while the cover is off the pool and tears caused by people or animals.
• Registration may be required. Blue Wave’s cards say registration is required to claim warranty coverage and ask buyers to mail the card within 30 days of purchase.

So a 16 mil cover with a 7-year warranty is not a promise of seven seasons. It means the maker will share the cost of a replacement, on a sliding scale, if the layers separate or a seam fails under normal use.

What thickness does not fix

Several of the ways a solar cover wears out have nothing to do with mil rating. Blue Wave’s 8 mil and 12 mil instructions carry the same care rules, and the D.E.I. sheet below sets similar rules without naming a thickness.

• Sun while the cover is off the water. Blue Wave’s instructions say the blanket must be protected from sunlight when it is removed from the pool, by placing it in the shade or covering it with a white opaque cover, and that delamination from direct sun while off the pool voids the warranty. The D.E.I. solar cover warranty and instructions (hosted by Doheny’s) say a rolled or folded cover, on the water or not, must be kept out of the sun.
• Hot water. Blue Wave says water above 90°F may shorten the blanket’s life and the blanket should be removed when the pool rises above that. The D.E.I. sheet says not to use the cover above 90 degrees.
• Shocking the pool. The D.E.I. sheet says to remove the cover when shocking and not to put it back within 8 to 10 hours after super chlorinating. Blue Wave’s warranty excludes damage from excessive chlorine exposure. Follow your chemical labels for the water itself; these are cover-care rules, not swimming guidance.
• Winter. Blue Wave says not to leave the blanket on after the swimming season ends, because it is not a winter cover.

Under Blue Wave’s and the D.E.I. instructions, a cover left baking on a concrete deck while it is off the pool is outside the warranty, whatever its thickness. In The Swim’s 8, 12, and 16 mil pages also exclude sun damage while the cover is off the pool. If your routine makes those habits hard to avoid, a thinner cover you replace sooner may be the better value.

Weight and handling: the cost of extra mil

More plastic means more weight. In The Swim lists a product weight of 36 lb for its 16 x 32 ft Ultra 16 mil cover. Its 8 and 12 mil pages for the same size do not list a weight, so a side-by-side comparison is not possible from the maker’s pages. The direction is still clear: at the same size, a thicker sheet carries more material, and a cover pulled off the pool with water pooled on top is heavier again.

That matters most when one person uncovers the pool by hand. Picture a 16 x 32 ft inground pool on a breezy afternoon: you drag the cover across the coping, fold it on the deck, and then need a shaded spot for it. Blue Wave’s instructions say to lift the blanket carefully over abrasive decks, coping, or any sharp, ragged surface. In The Swim’s pages say adding a solar cover reel makes removing and applying the cover more convenient and helps reduce wear and tear. If you own a large pool and plan to use a reel, the extra weight of 14 or 16 mil is less of a problem.

12 mil vs 16 mil solar cover

This is the comparison most buyers end up making, and the In The Swim pages show that the two covers differ in more than thickness. The 12 mil Premium is blue. The 16 mil Ultra is grey, and its page says the bottom layer is aluminized. The 16 mil page carries a 7-year warranty, the 12 mil page a 5-year warranty in its feature list. Only the 16 mil page lists a weight.

Because the color and backing change along with the thickness, you cannot read any difference in warming between these two covers as an effect of mil alone. Some product pages state how many degrees a cover can raise water temperature, but those are the makers’ own claims, they differ by color and design, and this guide does not repeat them. Choose 16 mil over 12 mil for the longer warranty term and if you will use a reel. Choose 12 mil if you handle the cover by hand and want less weight to manage.

So what mil is best? Match it to your pool

The best pool solar cover thickness for your yard comes down to pool size, how you take the cover off, and how well you can store it. Start with the situation that sounds most like yours.

• Small above ground pool, uncovered by hand most days. For a 15 ft or 18 ft round pool, Blue Wave offers both a blue 8 mil and a clear 12 mil blanket. Go 12 mil for the longer warranty, or 8 mil if keeping the cost down matters more.
• Large inground pool with a reel. A reel takes the weight off your arms, so a 12 to 16 mil cover makes sense, and the longer warranty terms come with it.
• Large inground pool, no reel, one person. Weigh the handling before the warranty. A 12 mil cover is a reasonable middle ground. Plan on a shaded storage spot either way.
• Windy yard. Fit matters more than thickness. Blue Wave’s instructions say a correctly cut cover, bubble side down, should float in place through wind and heavy rain without grommets, ties, or weights. Trim it carefully before you blame the mil rating.
• Hot climate or frequent shocking. If your water often runs above 90°F or you shock the pool often, the cover will spend more time off the water, and Blue Wave’s and the D.E.I. instructions say a cover off the pool must be kept out of the sun. Thickness does not change that, so put the effort into shade and storage.
• Tight budget. In The Swim describes its 8 mil covers as made for buyers who want a long-lasting cover within a set budget. Expect the shorter warranty that comes with it.

Where the sources stop

None of the maker pages reviewed for this guide gives a lifespan in seasons for each thickness, and none gives a heating difference that comes from thickness alone. The warranty term is the only sourced number that changes with mil, and it is prorated and limited to two defects. Treat any claim that a certain mil “lasts” a set number of years as an estimate, unless the maker puts it in writing.

Thickness is also only one part of using a cover well. Placing it bubble side down, trimming it to fit, taking it off fully before anyone swims, and storing it out of the sun are the basics of how to use a solar pool cover, whatever its thickness. If you are still choosing between cover types for the off season, a solar cover is not part of the mesh vs solid pool cover decision, because it is not a winter cover. You can browse other cover guides in the Pool Covers section.

FAQ

How thick should a solar pool cover be?

For most backyard pools, 8 to 16 mil covers the range makers sell. Pick 8 or 12 mil if you handle the cover by hand on an above ground pool, and 12 to 16 mil for a large inground pool with a reel. The thicker covers in the lineups reviewed here carry longer, prorated warranties.

Is a 12 mil or 16 mil solar cover better?

Neither is better for every pool. In The Swim’s 16 mil cover carries a 7-year warranty against 5 years for its 12 mil cover, but it is a heavier sheet with a different color and an aluminized bottom layer. Choose 16 mil with a reel, and 12 mil if you pull the cover by hand.

Does a thicker solar cover heat the pool more?

The maker pages reviewed here do not separate heating from thickness. Covers of different mil ratings also differ in color and backing, so any difference in warming cannot be tied to mil alone. Blue Wave’s instructions note that a clean blanket is more efficient than a dirty one.

Does a thicker solar cover make the pool safer?

No. Blue Wave’s instructions say its solar blanket is not a safety device and must be removed before swimming, and the CPSC says solar covers do not provide protection from drowning. Keep a fence, a self-latching gate, and an adult watching, as CPSC’s Pool Safely tips recommend.

How long does a solar pool cover last?

Makers do not publish a lifespan per thickness. The warranty terms (3 years for 8 mil up to 7 years for 16 mil in the lineups above) are the best sourced guide, and they are prorated. Blue Wave’s instructions say sun exposure off the pool can void the warranty and that water above 90°F and high chlorine can shorten a blanket’s life.

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