How Does an Igloo Stay Warm Without Melting?

Igloo Basics

Igloos are domes built out of blocks of hard-packed snow. These snow blocks are harder than powdery snow, but they still have trapped air-bubbles inside. An igloo usually has a small tunnel as an entrance, which keeps it warm inside. They can vary from small shelters just big enough for one person to curl up inside to fairly large domes big enough to hold 20 people or more. They can also vary in internal temperature from around 19 to above 60 degrees F.

Melting Ice

Since water melts at 32 degrees F, it seems like igloos should melt. In fact, they do, very slowly, but they refreeze again, since ice does not instantly turn to water at 32 degrees F. Water conducts heat very efficiently, but an ice cube in a drink can take half an hour or more to absorb enough heat to melt.

Freezing Igloos

As the ice crystal in a snow block melt, they are slowed by the pockets of cold air around them. Additionally, they channel some of the heat to the outside of the igloo. As the heat inside melts the surface of the wall, the air outside--often much colder than the air inside--freezes it. The igloo ends up with a strong sheet of ice on the inside. This strengthens it, and adds to the insulation.

Resources

• Read this Article in Spanish
• How to Build an Igloo