How the Modern Waterbed Works

A 1971 patent describing a liquid-filled, heated furniture support designed to cradle human bodies without letting them touch the bottom of the container.

What it covers

The patent describes a furniture support, specifically a sofa or bed, that uses a flexible, inelastic bladder filled with liquid to support multiple people. The system requires a rigid frame to hold the liquid and prevent the sides of the bladder from bulging outward. A key feature is that the bladder is filled completely, leaving no air inside, which allows the surface to conform to the body's shape while ensuring the person remains suspended by the liquid. It also includes an optional heating element to keep the liquid at a comfortable temperature and solid particles like styrofoam to stop the liquid from sloshing around when someone moves.

What it doesn't cover

• —Does not cover air mattresses or inflatable supports that rely on gas rather than liquid.
• —Does not cover waterbeds that allow the user to touch the bottom surface (the patent requires the body to be supported entirely by the liquid).
• —Does not cover flexible bladders that are not contained within a rigid lateral framework.
• —Does not cover liquid supports that contain significant amounts of air within the bladder.

The clever bit

The invention solves the 'bottoming out' problem by using a rigid frame to force the liquid to support the body's weight, and it uses internal particles to dampen the wave motion that would otherwise make a multi-person bed unstable.

Why it matters

This patent is a foundational document for the commercial waterbed industry, which saw a massive surge in popularity during the 1970s and 1980s. By defining the specific requirements for a stable, heated, and comfortable liquid-support system, it helped transition the waterbed from a niche DIY experiment into a standardized piece of home furniture.

Real-world examples

• 1.Traditional hardside waterbeds
• 2.Heated liquid-filled furniture
• 3.Medical fluid-support mattresses for pressure sore prevention