In regions where winter temperatures can plunge below −30 °C, Indigenous Arctic communities have long relied on igloos—domed shelters built from compacted snow and sometimes ice—to create surprisingly warmer microclimates indoors. While the walls are literally frozen, the air inside can rise to around 0 to 15 °C, warmed by body heat, small lamps, and even the presence of animals such as sled dogs or mice. This article examines the thermodynamics behind igloos, how they keep occupants warm, and what modern scientific research and traditional knowledge reveal about their performance.


What Is an Igloo and How Is It Built?

The word “igloo” comes from the Inuktitut word iglu, meaning “house” or “dwelling,” and historically referred to various types of homes, not only snow domes. In popular usage today, an igloo generally means a temporary or semi‑permanent shelter made of snow blocks, used traditionally by Inuit and other Indigenous peoples of the Arctic, especially in areas of Canada and Greenland.

According to descriptions compiled by anthropologists and Arctic explorers cited by the Canadian Encyclopedia, igloos are typically:

  • Constructed from wind‑packed or cut snow blocks, often about 40–60 cm long.
  • Built in a spiral pattern, with blocks leaning inward to form a self‑supporting dome.
  • Equipped with a low entrance tunnel and a slightly raised sleeping platform.
  • Sometimes lined or modified with animal skins, ice windows, or additional snow packing.

These design features are not primarily aesthetic; they are functional, directly influencing how heat is generated, stored, and lost inside the igloo.

Interior of a traditional snow igloo, showing the curved snow walls, raised sleeping platform and low entrance. Image: Wikimedia Commons / Public Domain.

The Basic Thermodynamics: Why Ice and Snow Can Insulate

At first glance, it seems contradictory that a structure made of frozen water could keep anything warm. From a thermodynamics standpoint, the key is not that snow is “warm,” but that it is a poor conductor of heat and traps air.

Snow as an Insulator

Fresh or compacted snow contains a large amount of still air trapped between ice crystals. Air, when it cannot move freely, is a very poor conductor of heat. Laboratory measurements summarized by the U.S. Environmental Protection Agency and other technical sources typically place the thermal conductivity of snow between about 0.05 and 0.3 W/(m·K), depending on density and moisture content. That is closer to commercial insulation materials than to solid ice or rock.

“The low thermal conductivity of snow arises largely from its high porosity and the insulating effect of trapped air.” — Snow and Ice-Related Hazards, Risks, and Disasters, Elsevier, 2015.

Solid ice conducts heat several times more effectively than dry snow. For insulation, snow blocks are therefore preferable to clear ice blocks because they slow the escape of heat from the warmer interior to the colder exterior.

Heat Flow and Temperature Difference

Thermodynamically, heat flows from warmer regions to colder ones. For an igloo, that means:

  • The warm side is the interior, warmed by human bodies, animals, and small heat sources.
  • The cold side is the exterior air and wind, often far below freezing.
  • The snow walls act as a thermal resistor, slowing the rate of heat loss.

In steady‑state conditions, the internal temperature reaches a balance where heat gained from occupants and other sources equals the heat lost through conduction, ventilation, and small openings.


Where the Heat Comes From: People, Animals and Small Fires

Igloos do not generate heat on their own; they only retain what is produced inside. Measurements by field researchers and model calculations reported in journals such as the Journal of Hydrometeorology and related literature suggest that:

  • An adult human at rest produces roughly 70–100 W of heat.
  • Small animals (such as a mouse) emit only a fraction of that but still contribute some heat.
  • Oil lamps, candles or small stoves can add tens to a few hundred watts of heat, depending on size.

In a small igloo, a family of several people and a small lamp can collectively produce a few hundred watts of heat—enough to raise the indoor temperature significantly above outside levels when paired with effective insulation.

How Much Can a Mouse Warm an Igloo‑Like Space?

While traditional accounts focus on human occupants and dogs, the same principles apply at small scales. A mouse typically generates only about 1 W of metabolic heat. In a full‑size igloo, that contribution would be negligible. However, in a tiny snow burrow or “micro‑igloo” closer to a mouse’s body size, the heat can be more significant.

Biologists studying small mammals in cold climates, as summarized in works such as Life in the Cold: Evolution, Mechanisms, Adaptation, and Application (Springer), note that rodents often create insulated nests in snow, grass or underground to trap their own metabolic heat. In these confined spaces, with walls that slow heat loss, a small animal can maintain a temperature above freezing even while the ambient air is far colder.

The thermodynamics for a mouse in a snow burrow and a person in an igloo are similar:

  • Heat is produced by metabolism.
  • Heat escapes via conduction through walls and by ventilation.
  • A balance is reached where the interior stabilizes at a temperature that allows survival.

Design Features That Help Igloos Keep Warmth

Beyond the insulating properties of snow itself, details of igloo design exploit basic physics to improve thermal comfort.

1. Dome Shape and Structural Stability

The dome shape distributes compressive forces from the snow blocks evenly, making the structure strong enough to resist wind and the weight of accumulated snow. From a thermal perspective, the dome minimizes surface area for a given volume, which reduces total heat loss. A sphere has the smallest possible surface area for a given volume; a dome approximates this.

2. Raised Sleeping Platform and Cold Air Sump

Warm air is less dense and rises, while cold air sinks. Many igloos, according to ethnographic accounts and engineering analyses, incorporate:

  • A low entrance tunnel that is slightly below the main floor.
  • A raised sleeping or sitting platform inside.

Cold air entering the igloo tends to settle in the lower part near the entrance, forming a “cold sump.” Warmer air collects in the upper part where people sleep and work. This stratification improves comfort without requiring additional energy.

3. Air Exchange and Moisture Control

Completely sealing an igloo would reduce heat loss but create the risk of carbon dioxide buildup and high humidity from breathing and cooking. For safety and comfort, builders typically leave small ventilation holes near the top or use porous snow to allow slow air exchange.

Ventilation increases convective heat loss but prevents condensation from saturating the snow walls. If snow becomes too wet, its thermal conductivity rises, reducing its insulating ability. Balancing ventilation and insulation is therefore an important practical consideration.

4. Partial Melting and Refreezing

When a small heat source such as a lamp is used, the inner surface of the igloo may warm slightly above 0 °C and then refreeze. Canadian engineer and explorer accounts, as well as later analyses, report that this process can create a thin ice crust on the interior surface.

Opinions differ on whether this is beneficial. Some researchers argue that a thin ice layer:

  • Increases structural strength by bonding blocks more firmly.
  • Reduces air infiltration through gaps.

Others note that solid ice is a better conductor than dry snow, so an extensive ice crust could increase heat loss. In practice, the effect depends on thickness, extent and the trade‑off between air‑tightness and conductivity.


How Warm Does an Igloo Actually Get?

Reports of igloo temperatures vary, reflecting differences in climate, wind, igloo size and occupancy. Historical accounts from Arctic expeditions and more recent fieldwork generally describe the following patterns:

  • Outside air temperature: often between −20 °C and −40 °C during winter storms.
  • Interior air temperature with people only: commonly between −5 °C and +5 °C.
  • Interior air temperature with people and a small lamp or stove: occasionally reaching +10 to +15 °C.

For example, a field study referenced in engineering texts on cold‑region design describes igloo interiors stabilizing just below freezing with only human occupants, and slightly above freezing when additional heat sources were used. The Encyclopaedia Britannica notes that the temperature can rise to around 16 °C (60 °F) when an igloo is occupied and heated moderately, while outside temperatures remain far below freezing.

Comfort Versus Survival

Modern readers accustomed to heated homes may not view 0–10 °C as “warm.” However, for people wearing suitable Arctic clothing and used to outdoor conditions, this represents a substantial improvement in thermal stress. The primary purpose of an igloo historically has been:

  • To reduce wind chill and convective heat loss.
  • To keep the environment above dangerously low temperatures.
  • To provide a stable, relatively mild microclimate for rest, work and sleep.

In this context, igloos can be described as effective survival shelters whose insulating performance is well supported by both experience and thermodynamic principles.

A snow igloo in an Arctic landscape highlights the contrast between severe outdoor cold and the more stable conditions inside. Image: Wikimedia Commons / CC BY-SA 3.0.

Scientific Debates and Comparisons With Modern Insulation

While the basic physics of igloos is widely accepted, researchers and engineers have discussed several points where perspectives differ.

How Efficient Is Snow Compared With Modern Materials?

Some building‑science authors highlight that snow’s thermal resistance (R‑value) per unit thickness is modest compared with high‑performance foams or fibrous insulation used in contemporary construction. From this view:

  • Snow walls must be relatively thick to achieve the same insulation as modern materials.
  • Heat loss through conduction remains significant, especially in thin‑walled or partially melted structures.

Others emphasize context: in treeless, resource‑limited Arctic environments, snow is abundant, free and quickly assembled with available tools. In this perspective, igloos represent an efficient use of local materials, even if they are not comparable to modern insulated buildings in absolute performance.

Role of Ice Layers: Help or Hindrance?

As noted earlier, the role of interior ice crusts is debated:

  • Supportive view: A thin ice shell increases tensile strength and reduces infiltration, which can outweigh the slightly higher conductivity of ice relative to snow.
  • Critical view: If too much snow melts and refreezes as dense ice, the overall wall becomes a better heat conductor, eroding the igloo’s insulating effectiveness.

Field experience from Indigenous builders often favors maintaining dry, compact snow and avoiding excessive interior heating that could destabilize the structure.

Scaling Down to Animal Shelters

Researchers in animal physiology note that many cold‑adapted species use strategies analogous to igloos—including snow burrows, dens and insulated nests. However, not all scientists agree on the relative importance of such shelters versus biological adaptations like fur, fat layers and metabolic regulation.

Some studies argue that micro‑shelters mainly reduce wind exposure and provide modest temperature increases, while others show that, especially for small mammals, enclosed spaces can drastically cut heat loss due to their high surface‑area‑to‑volume ratio. Despite these discussions, there is broad agreement that any shelter, including a simple snow cavity, improves energy balance in cold conditions.


Step‑by‑Step Thermodynamic Walkthrough

The operation of an igloo can be outlined as a sequence of energy flows.

  1. Heat Generation: Humans, animals and small fires continuously convert stored chemical energy (food or fuel) into heat. For a small family inside an igloo, the total heat output may reach several hundred watts.
  2. Heat Storage and Air Warming: This heat warms the air, interior surfaces and occupants. Because the snow walls are cold and massive, they absorb some heat but warm relatively slowly.
  3. Heat Loss Through Conduction: Heat flows through the snow walls from the warmer interior to the cold exterior. The rate depends on the temperature difference, wall thickness and snow’s thermal conductivity.
  4. Heat Loss Through Ventilation: Some warm air escapes through the entrance and ventilation holes, replaced by cold outside air. This convective loss is necessary to maintain breathable air.
  5. Equilibrium Temperature: After some time, the igloo reaches a steady state: the heat produced inside equals the heat lost. The interior temperature at this point is often just below or above 0 °C, depending on conditions and heat input.

For a mouse or other small animal in a tiny snow burrow, the same sequence applies on a smaller scale. The animal’s relatively large surface area causes rapid heat loss in open air, but surrounding snow reduces this loss, allowing its limited heat production to maintain a survivable local temperature.




Conclusion: How Ice Houses Help Keep Occupants Warm

From a thermodynamic perspective, the ability of an igloo to keep people or animals warm rests on familiar physical principles: low thermal conductivity of snow, controlled airflow, and the continuous generation of metabolic or combustion heat inside a confined space. Snow walls slow the escape of that heat, while design features such as domed geometry and raised sleeping platforms help distribute it more effectively for human comfort.

Historical experience from Indigenous Arctic communities and modern scientific analyses largely converge on the same conclusion: within their environmental and cultural context, igloos function as practical, efficient shelters. Whether scaled up for human use or down to the size of a mouse’s snow burrow, the underlying physics of staying warm in a structure built from ice and snow is consistent and well understood.