Properties of Expanding Acoustic Foam

Written by wes walcott
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Expanding foam is a product that is designed to harden after being applied to the desired surface. There are quite a few different types of expanding foam available to consumers today, and they can serve a number of purposes ranging from insulation to cast-making. For those looking to build a music room or soundproof their house, expanding acoustic foam is probably the best option.


Most acoustic foams are open-celled. This means that the foam is porous, allowing for liquid water and water vapour to permeate the insulation.

Fire Retardant

By increasing air resistance, expanding acoustic foam has the effect of lessening the intensity of sound waves in the air. However, because the energy from the reduced sound waves is dispersed as heat, acoustic foam needs to be treated with fire retardants.

Reflection and Absorption

Quality acoustic material is designed so that it has a low-reflection upper surface combined with a very dense, high-absorption lower mass. This allows most of the sound energy to be captured within the upper layer while any remaining sound energy that reaches the lower mass will be converted to thermal energy.

High Sound Transmission Class

The sound transmission class, or STC, is a rating given to materials based on their ability to absorb acoustic energy. The higher the STC is, the better the material is able to absorb acoustic energy.

Hardening Time

The typical hardening time for most expanding foam is in the range of five to 12 hours. However, this is largely dependent on current temperatures and humidity levels.

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