Resilient underlayment: definition and role

What is a resilient underlayment?

A resilient underlayment is a flexible layer placed between the subfloor and the screed, designed to absorb and dissipate vibrational energy rather than allowing it to transmit into the structure. It acts as the spring in the mass-spring-mass system that defines a floating floor.

It comes in rolls, sheets, or panels made from various materials, such as technical foams, mineral fibers, cork, or recycled rubber. The material itself matters less than its mechanical behavior.

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Resilient does not mean soft

This is the most common misconception. A resilient material must be able to deform under vibration and then return to its original shape, repeatedly, for years.

A simply soft material will crush and fail to recover. Once compressed under the weight of the screed and furniture, it loses its elasticity and stops acting as a spring. The floor becomes rigid again without anyone noticing, until the noise returns.

The key metric is dynamic stiffness. The lower it is, the more effectively the underlayment decouples the floor. It is independent of thickness, which explains why a thin product can outperform a thick one.

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How to interpret performance

Manufacturers advertise impact noise reduction in decibels. This value indicates the gain provided by the underlayment compared to a reference floor measured in a laboratory.

Two caveats apply to this figure. It is obtained on a standardized slab, which may not match actual site conditions. Furthermore, it assumes perfect installation without any sound bridges. In practice, a high-performance underlayment installed poorly will yield worse results than an average one installed correctly.

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Compressibility: an often overlooked constraint

An underlay must provide decoupling, but it must also provide support. If it is too compressible, it allows the screed to flex under loads and crack. This is why the choice of underlay and the calculation of the screed thickness must be done together, never separately.

A floating screed installed on an underlay that is too soft without compensating for thickness is a classic cause of cracking in renovation projects.

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Where it fits into the system

It is placed on the substrate, after the waterproofing film if required, and before the screed. The strips are laid edge-to-edge, sometimes covered with a protective film to prevent the liquid screed from seeping between them.

It must be paired at the edges with a perimeter strip installed vertically. Without it, the screed touches the walls, creating a sound bridge and rendering the underlay useless. We combine these materials with our screeds as part of our acoustic solutions.