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Before humans invented EPS insulation, animals already understood the importance of good insulation.

A rabbit prepares its resting place with grass and fur — thin, but carefully planned. It never lies directly on bare ground. Before hibernation, a bear does not simply lie down on the bare floor of a cave. It brings dry leaves, grass, moss and twigs to create a soft layer up to 30 cm thick, separating itself from the cold earth.

Its instinct follows one simple rule: the ground steals your heat. Every calorie the body uses to stay warm is one less calorie available to survive the winter.

Neither animal has attended a course in building physics. Neither has prepared an energy performance certificate for its shelter. Yet both instinctively understand that there should be as thick an insulating layer as possible between them and the cold ground.

Bear Mathematics, Translated into Building Physics

What a bear does is not just a vivid metaphor — it can be measured as effective insulation.

The materials in a bear’s bedding have a very low thermal conductivity, with a lambda value of approximately 0.05 W/mK. A 30 cm-thick bedding layer can therefore achieve a thermal transmittance value of around U = 0.17 W/m²K.

That is almost twice as good as the performance achieved with 10 cm of EPS insulation beneath the foundations of a house, which has a U-value of approximately 0.32 W/m²K.

Put simply, a bear instinctively creates almost twice as much insulation performance as a standard 10 cm layer of EPS beneath a foundation slab. The obvious question is: would a bear be satisfied with our 10 cm?

Why This Is More Than Just an Interesting Fact

This comparison highlights something that can be easy to overlook in building physics: how much insulation is “enough” is a matter of degree, not an absolute answer.

A standard 10 cm layer of EPS beneath a foundation slab reduces the floor’s thermal transmittance from around U = 1.0 W/m²K for an uninsulated slab to approximately U = 0.32 W/m²K. This is a major improvement — but it is still less than what a bear naturally creates using materials found in nature.

That is why, in certain cases, we recommend 20 cm of EPS insulation instead of 10 cm. This can further reduce heat losses through the floor by 40 to 50%.

When is this most worthwhile?

• When the house is located in a colder area, such as a mountain region where the ground beneath the foundations is much colder than in coastal areas
• When you have or are planning underfloor heating, which can lose significantly more heat through a poorly insulated slab due to the higher floor temperature
• When you are aiming for Eko Fund incentives or a nearly zero-energy building standard

Why This Decision Is Permanent — Just Like Every Winter for a Bear

A bear can make its bedding thicker every year if it needs to. A homeowner does not have that option.

You can replace windows later, renovate the façade or repair the roof. But once the house has been built, you cannot add insulation beneath it — not even one centimetre.

That is why choosing the thickness of insulation beneath the foundation slab is one of the few truly permanent decisions in home construction. It must be made before the concrete is poured, not after moving in.

What You Gain by Making the Choice a Bear Would Make

It is not only about a lower heating bill, although that is often the most tangible reason. A well-insulated foundation slab also means:

• Warmer floors every day — more comfortable for children playing on the floor and for bare feet in the morning
• Less sensitivity to future energy price increases
• A better energy performance certificate and, as a result, higher long-term property value

A bear does not build its bedding because someone will inspect the energy performance certificate of its den. It does so because surviving winter should not be left to chance.

The logic is surprisingly similar when building a home — except that instead of survival, we are talking about the comfort you will feel every day for the next 50 years.

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Stela Haus Academy creates educational content for future prefabricated-home owners because we believe every investor deserves to understand what truly matters. Send us your questions about foundation insulation at office@stelahaus.com.