Warmth is a relative term, especially if you consider near freezing temperatures as warm. Igloos can certainly keep you warmer compared to the cold outside. By how much?
Noah Talansky, a Meteorologist answered the question. Even if the outside temperature drops to -50 degree Fahrenheit , a well built Igloo can maintain a temperature of near freezing or 32 degrees Fahrenheit when aided by body heat and other sources of heat.

Two aspects, design and insulation is the key.

Insulation.

You have to know your snow. Eskimos certainly do. There are about 50 words in Eskimo language for snow. They describe various kinds of snow. A block of ice which is quite solid does not contain much in the way of trapped air. It is the pockets of trapped air in snow that provides insulation. Eskimos use compressed snow which has a lot more air pockets, to form blocks which are then laid down to form the Igloo shape. These blocks provide fantastic insulation.

Design aspects.

• The entrance to an Igloo often has at least one 90 degree turn.
  

  
  This prevents cold air from blasting into the interior.

• The top an Igloo usually has a small opening to let out excess heat and smoke if a smoke producing heat source is used. The idea is to prevent excess heat from forming which otherwise would start melting the structure.

• The arch shape of an Igloo provides stability to the structure.

• The inside of an Igloo may have levels with living quarters in the middle or towards the top. Cold air moves downwards and warmer air rises. So it is warmer in the upper levels an Igloo.

Even simple heat escaping from a human body can warm up an Igloo. A fire source is also often used.

A great video on the subject can be found here.

Never knew there was an Igloo hotel!

All images courtesy of Pixabay.