Cold plunges naturally create dramatic temperature differences between the inside of the cold plunge and the outside surrounding environment. When that cold surface meets warm, humid air, condensation forms, often collecting beneath the plunge. Even when placed on a “waterproof” mat, moisture can become trapped underneath, leading to mold, mildew or flooring damage.
Why Waterproof Mats Aren’t Enough
A waterproof mat stops water from soaking into the floor, but it doesn’t stop moisture from forming underneath it. In fact, these mats can trap condensation. As the cold plunge chills the air directly below it, moisture accumulates, gathers on the underside of the mat, and has nowhere to evaporate.
The Key: Create an Air Gap
The most effective solution is to ensure consistent airflow beneath the tub. Adding a layer of spacing material—like wooden slats, composite decking strips, or a purpose-built equipment riser—between the plunge and the mat allows air to circulate. This airflow promotes evaporation and prevents moisture from lingering.
Recommended Setup
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Start with a waterproof mat to protect the floor from splashes.
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Add a raised platform on top of the mat:
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Wooden slats
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Plastic/composite deck tiles
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A slatted equipment platform
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Place the cold plunge on the raised surface, ensuring at least ½–1 inch of space beneath.
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Check airflow around the perimeter—don’t push the plunge fully against a wall.
Extra Tips
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Lift and inspect the platform every few weeks.
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If indoors, a dehumidifier can reduce humidity at the source.
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A small fan can also help in drying out the area.
By giving moisture an escape route and letting air circulate freely underneath your cold plunge, you eliminate trapped condensation to keep the bottom of your cold plunge and the surface it stands on clean, dry, and mold free.
