Foam-free • Six sizes • Fits square spas 77″–94″
The Ultimate Hot Tub Replacement Cover: Thrml AIRCAP 1™
Most hot tub replacement covers use the same design that failed you last time: a foam core wrapped in vinyl. Over the years that foam soaks up water, sags and gets so heavy you dread lifting it. The Thrml AIRCAP 1™ has no foam at all. It is an inflatable, drop-stitch spa cover with AirLoc™ construction, a zip-on ZipTech™ skirt system and an included pump, and it takes about 10 to 15 minutes to set up.
It comes in a full range of sizes that fit square spas from all major brands. It does not absorb water, so it won't warp or get heavier over time. This could be the last hot tub cover you ever need to buy.
Order NowFree shipping within the contiguous USA • 3-year manufacturer warranty
What is the best hot tub replacement cover for a square spa?
If you have a square hot tub between 77″ and 94″ and you're tired of heavy, waterlogged foam, the Thrml AIRCAP 1™ is a strong choice. Instead of foam, it uses air held inside welded drop-stitch panels. Thrml says the core absorbs 0% water and the cover weighs about 35–40 lbs, depending on size, for its whole life. According to Thrml, the cover often lasts 10–15+ years with proper care, compared with the typical 3–5 years for a foam cover.
Why Most Hot Tub Covers Need Replacing, and Why This One Is Different
A traditional foam spa cover works well when it is new. But steam, spa chemicals, UV rays, rain and small punctures slowly get through the vinyl and vapor barrier. The foam starts absorbing moisture. According to Thrml, a foam cover can take on 75–150+ lbs of water over time. As it does, it gets heavier, sags in the middle, can grow mold and mildew, and loses much of its insulating value.
The AIRCAP 1™ avoids all of that because there is no foam inside to fail. It is foam-free, so it doesn't take on water, and it stays light enough for one person to open and close every day.
The Technology Inside the AIRCAP 1™ Spa Cover
AirLoc™ Drop-Stitch Construction
Two layers of reinforced fabric are joined by thousands of welded polyester threads. It's the same idea used in rigid inflatable paddleboards. When the cover is inflated, it becomes a firm, flat panel that resists punctures, tears and UV damage.
Steady Insulation Over Time
The 3″ insulating core traps still air, a natural insulator. Because it never gets waterlogged, Thrml says the cover keeps its insulating value for its whole life. That means less heat loss, less evaporation and lower energy costs.
ZipTech™ Replaceable Skirts
A waterproof zipper system attaches the skirt. Three skirt lengths are included, so you can get a close, semi-custom fit on your spa cabinet. If a skirt ever wears out, you just replace the skirt, not the whole cover.
Pressure Release Valves
Patent-pending pressure release valves (PRVs) handle air expansion caused by heat and temperature changes. They prevent over-inflation and protect the seams through hot summers and freezing winters.
Easy Setup, Shipped to Your Door
Custom foam covers can take weeks to build. The AIRCAP 1™ ships in a single box, straight to your door, ready to install. Everything you need is included:
- Two inflatable AIRCAP 1™ cover halves
- Dual-action pump
- Three interchangeable ZipTech™ skirt lengths
- Four tie-down straps with locking buckles
Setup in 4 steps: inflate both halves with the pump, choose the skirt length that fits your cabinet, zip the skirt on, and set the cover on your spa. Thrml estimates setup takes 10–15 minutes.
Free shipping within the contiguous USA • 3-year manufacturer warranty
Foam Hot Tub Covers vs. Thrml AIRCAP 1™
Before you replace your hot tub cover, it helps to compare what you'll own in year one with what you'll own in year five.
| Feature | Traditional foam cover | Thrml AIRCAP 1™ |
|---|---|---|
| Core | EPS foam wrapped in vinyl | Pressurized air in welded drop-stitch fabric |
| Water absorption | Absorbs water through cracks, punctures and failed seams | 0% – no porous core for water to enter |
| Weight over time | Starts light, can gain 75–150+ lbs of water | About 35–40 lbs, the same from day one |
| Insulation | Drops as foam waterlogs and sags | Stays consistent for the life of the cover |
| Shape | Warps, sags and cracks | Rigid, flat panel that holds its shape |
| Mold & odor | Common once foam is saturated | No porous material inside to hold moisture |
| Typical lifespan | 3–5 years | Often 10–15+ years with proper care |
| Estimated annual energy cost* | $400–$600 | $280–$420 |
| Skirt | Sewn on; damage often means a new cover | Zip-on and replaceable, with 3 lengths included |
*Manufacturer estimates based on average U.S. energy rates and typical hot tub use. Your actual savings will vary. Lifespan and weight figures are from Thrml.
How to Find Your Hot Tub Cover Size
The AIRCAP 1™ comes in six sizes for square spas from 77″ to 94″. Thrml says the range covers current square models from every major hot tub brand. Sizing takes about a minute:
- Measure the outside length and width of your spa at the top edge. You can also measure an old cover that still fits well.
- Match that measurement to a size in the chart.
- Fine-tune the fit on install with one of the three included skirt lengths.
Measuring between two sizes? Measure your current cover if it still fits well, and pick the size range your spa falls into. The three included skirt lengths take care of the rest.
| AIRCAP 1™ size | Fits square spas | Color |
|---|---|---|
| XX-Small (XXS) | 77″ – 79″ | Deep Grey |
| X-Small (XS) | 80″ – 82″ | Deep Grey |
| Small (S) | 83″ – 85″ | Deep Grey |
| Medium (M) | 86″ – 88″ | Deep Grey |
| Large (L) | 89″ – 91″ | Deep Grey |
| X-Large (XL) | 92″ – 94″ | Deep Grey |
Free shipping within the contiguous USA • 3-year manufacturer warranty
Built for Every Season, Designed with Safety in Mind
Thrml has tested the AIRCAP 1™ against golf balls fired at 160 mph to simulate hail, heavy snow loads, extreme heat and below-zero temperatures. The polyurethane-coated exterior resists UV rays and spa chemicals, and it wipes clean easily.
It is designed as a manual safety cover intended to meet ASTM F1346-23, the current standard for spa and hot tub safety covers. Heat-welded straps and keyed, lockable buckles keep it securely closed when the spa isn't in use.
3-Year
Limited manufacturer warranty against defects in materials and workmanship
0%
Water absorbed by the core, according to Thrml
35–40 lbs
Typical weight, depending on size, for the life of the cover
Free Shipping
To your door within the contiguous USA
Hot Tub Replacement Cover FAQs
How do I know when my hot tub cover needs to be replaced?
Replace your cover when it becomes hard to lift, sags in the center, smells musty, has cracked or torn vinyl, or no longer holds heat. Rising energy bills and more steam escaping around the edges are other common signs. These problems usually mean the foam core is waterlogged.
How long do hot tub covers last?
Foam hot tub covers usually last 3–5 years before water absorption makes them heavy and less effective. Because the Thrml AIRCAP 1™ has no foam to waterlog, Thrml says it often lasts 10–15+ years with proper care.
Will the AIRCAP 1™ fit my hot tub brand?
The AIRCAP 1™ comes in six sizes for square spas measuring 77″–94″. Thrml says these sizes cover current square models from every major brand. Measure your spa's outside length and width, then choose the matching size. The three included skirt lengths let you fine-tune the fit. It is not made for round, oval or irregularly shaped spas.
Is an inflatable hot tub cover as good as a foam cover?
The AIRCAP 1™ is not a soft, inflatable pillow-style cover. It uses rigid drop-stitch construction like a high-end paddleboard, with thousands of internal threads holding the panel flat and firm. A 3″ core traps still air for insulation, and because it never gets waterlogged, its performance doesn't fade the way foam does.
How much does the AIRCAP 1™ weigh?
About 35–40 lbs, depending on size. It stays at that weight for its whole life. A foam cover can gain 75–150+ lbs of water over time.
What comes in the box, and how long does installation take?
Each AIRCAP 1™ includes two inflatable cover halves, a dual-action pump, three ZipTech™ skirts in different lengths, and four tie-down straps. Most owners can inflate it, zip on a skirt and install it in about 10–15 minutes.
What warranty comes with the Thrml AIRCAP 1™?
Thrml backs the AIRCAP 1™ with a 3-year (36-month) limited warranty against defects in materials and workmanship under normal use. The warranty starts on the date of delivery to the original purchaser.
Make This the Last Hot Tub Cover You Buy
Stop replacing heavy, waterlogged foam covers every few years. Choose your size, and the Thrml AIRCAP 1™ ships free to your door, ready to set up in minutes.
Order NowFree shipping within the contiguous USA • 3-year manufacturer warranty
