The Hot Tub Cover That Doesn't Absorb Water

One of the many issues we set out to solve is the user experience for hot tub owners. Your hot tub should be a point of relaxation, not a stress. Foam hot tub covers deter owners from using their wellness products, and one of the main reasons why is 40-year-old hot tub cover technology.

Foam covers — the supposedly insulating protector of your very expensive investment — within months, sometimes even weeks, begin absorbing water. Every hot tub owner in the world has to deal with this, and eventually your cover becomes the deterrent to you and your family enjoying your spa. Whoever is tasked with preparing the hot tub and closing it down has to wrestle with an absurdly heavy, mold-infested, disgusting cover.

Our team of industry insiders heard you asking if there was anything better, and we built it. The AIRCAP 1™ is designed to have a consistent weight for the life of the cover, ensuring you and your family an incredible user experience — and we hope this encourages you to use your hot tub!

The AIRCAP 1™ hot tub cover from thrml.™ uses welded drop-stitch technology — a construction method featuring two layers of high-strength, reinforced fabric connected by thousands of tightly woven polyester threads. When inflated to the proper pressure, these threads hold the layers rigidly apart, creating a flat, structurally strong, fully sealed inflatable panel. This construction is best known in the rigid inflatable paddleboard industry.

The design is fully enclosed and airtight, with no porous core material exposed to the environment. The AIRCAP 1™ includes our patent-pending pressure release valves (PRV) to safely manage internal air expansion from heat or temperature changes, preventing over-inflation or stress on the seams while maintaining a consistent, sealed structure.

In stark contrast, traditional foam hot tub covers rely on a core of expanded polystyrene (EPS) or similar rigid foam wrapped in vinyl or a plastic vapor barrier. While the foam is theoretically “closed-cell” and the barrier aims to block moisture, real-world exposure to hot tub steam, chemicals, UV rays, rain, and physical wear inevitably compromises the system. Cracks, punctures, seam failures, or deteriorating tape and heat seals allow water vapor and liquid to penetrate. Once inside, the porous foam absorbs and retains moisture — often 75–150+ pounds per cover over time — causing it to become waterlogged, dramatically heavier, and prone to mold, mildew, and odors. Estimate what your foam cover weighs today.

From a water-absorption perspective, the AIRCAP 1™'s superiority is clear: its drop-stitch construction contains no absorbent foam core whatsoever — the interior is simply pressurized air held by impermeable fabric layers. This eliminates the root cause of saturation entirely, since air cannot absorb or retain water like porous foam does. The fully sealed, non-porous design keeps the cover lightweight (typically 35–40 lbs depending on size), maintains consistent performance, and avoids degradation issues like sagging, mold, or reduced insulation efficiency.

As a result, the AIRCAP 1™ delivers a significantly longer lifespan, easier handling, a better user experience, lower long-term costs, and reliable, constant thermal performance — without the recurring “heavy cover” problem that plagues traditional foam designs.