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Thermal Mass & Insulation: What You Need To Know

10 minutes
June 7th, 2021
Thermal mass vs insulation

When it comes to walling, cladding, flooring and other types of building materials, thermal mass indicates the material’s ability to absorb the surrounding heat energy and store it.

Thermal insulation, on the other hand, is defined as the reduction of heat transfer between objects.

But what exactly is the technical explanation of thermal mass and insulation in building design? What is the important connection between them? And what benefits do they both provide when used correctly?

In this article
What is thermal mass?
What is thermal insulation?
Why is high thermal mass important for insulation?
When used correctly, what are the advantages?
Ideal thermal insulation: important factors to consider

What is thermal mass?

Thermal mass plays a very important role in how thermal energy is transferred through a system, such as a residential home or a commercial building.

In technical jargon, ‘Cth’ is a system’s thermal capacitance (thermal mass) which is affected by the thermal energy being transferred known as ‘Q’ (thermal inertia), resulting in its ‘Δt or delta T’ (temperature change).

Basically, thermal mass relates to the way a material absorbs and stores its heat (energy). Materials with a lower thermal mass will change their temperature quickly, which means they aren’t the best for insulation. On the other hand, materials with a higher thermal mass will require a lot of heat to change their temperature, ideal for creating a thermal barrier.

What is thermal insulation?

Thermal insulation is the reduction of transferred heat between objects that differ in temperature and are in range of thermal contact or radiative influence.

Basically, thermal insulation acts as a shield against the entry and loss of heat (thermal loss) through conduction, convection and radiation. It creates a region of insulation where heat conduction is reduced (thermal lag).

Why is high thermal mass important for insulation?

A material with high thermal mass is able to absorb and store a large amount of heat and then slowly release it over time. This is important because it mitigates the effects of thermal bridging, which determines the rate of how energy (heat) is moved between the materials around it.

For example, compressed straw panels have a very dense core, resulting in the material having a high thermal mass. Because this gives them low thermal conductivity, heat cannot pass through them very easily and they act as a heat barrier, or thermal barrier, between both internal and external environments.

When installed inside of a home, the panels act as a thermal break, which prevents thermal bridging and provides a continuous layer of insulation. By reducing thermal loss, also known as heat loss, they provide an ideal way to regulate the inside temperature of a home.

High thermal mass materials can be a great way of absorbing the heat (solar energy) from the external environment during the day (solar gain), and then slowly release their stored heat inside the home during the night.

However, only with good insulation throughout the home can the benefits of high thermal mass materials be truly taken advantage of.

When used correctly, what are the advantages?

The rate of how a home’s temperature changes depends on how well it is insulated. In climates where there is a big variation in temperature (diurnal temperature) during the days and nights, such as Australia, thermal mass and insulation provide the most benefit when used in tandem.

These benefits can include:

  • Reducing home energy bills due to cooling and heating systems using less energy.
  • Creating a comfortable environment due to reduced internal temperature fluctuations.
  • Lowering greenhouse gas emissions due to reduced energy consumption.
  • Increased durability and extended life of building materials from the prevention of mould, humidity and other corrosive elements due to thermal insulation.
  • Improved sound insulation due to the incredibly dense core of high thermal mass materials.
  • Environmentally friendly as high thermal mass materials such as compressed straw panels are made from 100% sustainable material that is biodegradable.

Ideal thermal insulation: important factors to consider

As mentioned before, the benefits of high thermal mass materials can only be fully harnessed when combined with good insulation. So, what are some important factors to consider to get the best results out of thermal insulation?

To maximise the R-value (thermal resistance value), which was created to compare and rate different types of insulation material, it’s important to use the right materials combined with other factors such as having double glazed windows and blockout blinds.

This will establish an ideal thermal envelope, which is the combination of materials and structures of a building to create a barrier of insulation. The higher R-value a total system has, the greater the insulation power will be.

The climate of your surrounding environment and where/how thermal mass materials are installed inside the home can be a driving factor in how efficient the thermal insulation will be.

When living in a climate where the diurnal temperature can go from boiling hot during the day to freezing cold at night, insulation materials with high thermal mass are the most effective. Compressed straw panels, for example, provide protection from radiant heat and delay the flow of heat through a building, allowing for a cooler interior during the day and providing warm insulation at night.

Thermal conductivity is important when choosing which materials to install for insulation, as it measures how easily heat can travel through the material via conduction. Materials such as compressed straw panels have a lower figure and means they will provide a greater performance.

Along with thermal conductivity, thermal resistance also plays an important part. Featuring greater thickness with a dense core, compressed straw panels lower thermal conductivity by having less heat flow through the material.


Make sure you have a discussion with a trusted insulation installer or contractor to ensure that you are getting the best results with the best materials.

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