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Sweating Insulation Foam: How to Prevent It?

The Science Behind Sweating Insulation Foam

sweating insulation foam, condensation and water vapour

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Insulation foam is a versatile material commonly used to regulate temperature, reduce energy consumption, and enhance the comfort of buildings. While it is highly effective at maintaining the desired indoor climate, you might have noticed something perplexing – insulation foam sometimes appears to sweat. In this blog post, we will delve into the intriguing phenomenon of sweating insulation foam and uncover the scientific reasons behind it.

Understanding the Basics

Before we dive into the science, let's clarify what we mean by "sweating" in the context of insulation foam. Sweating, in this case, refers to the visible accumulation of moisture on the surface of insulation foam. This moisture can give the foam a damp or wet appearance, leaving homeowners puzzled about its origin.

Condensation: The Culprit Behind Sweating Insulation Foam

The primary reason for insulation foam to sweat is a process known as condensation. Condensation occurs when warm, humid air comes into contact with a surface that is cooler than the dew point temperature. When the air's moisture content (humidity) exceeds its capacity to hold water vapor, the excess moisture transforms from a gaseous state into liquid droplets – hence, condensation.

In the case of insulation foam, especially in climates with varying temperatures and humidity levels, condensation can occur when warm indoor air permeates through the foam and comes into contact with the cooler exterior surface of the foam. The foam's surface temperature is lower than the dew point temperature of the indoor air, causing the moisture to condense on the foam's surface.

Preventing Sweating Insulation Foam

1. Proper Installation: Ensuring insulation foam is installed correctly with airtight seals can help reduce the infiltration of warm, humid air into the foam structure, minimising the potential for condensation.

2. Vapour Barriers: Incorporating vapour barriers, such as plastic sheets or coatings, can limit the movement of moisture-laden air through the foam, reducing the chances of condensation.

3. Ventilation: Adequate ventilation is crucial to maintain balanced humidity levels within the living space. Properly designed ventilation systems can help expel excess moisture and minimise the conditions that lead to sweating insulation foam.


Sweating insulation foam may appear perplexing at first glance, but the scientific explanation behind this phenomenon is rooted in the principles of condensation. As warm, humid air interacts with cooler foam surfaces, moisture condenses, creating the appearance of sweat on the foam. To mitigate this issue and preserve the insulation's effectiveness, proper installation, the use of vapour barriers, and controlled ventilation play pivotal roles. By understanding the science behind sweating insulation foam, homeowners and builders can make informed decisions to create comfortable and energy-efficient living spaces.

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