"the heat in the igloos of my childhood"
Inside of an igloo
Public DomainInside an igloo - Credit: Canadian Geological Survey

 The word igloo commonly refers to snowhouses, although in fact iglu means simply 'a house' and can describe traditional tents, homes constructed of driftwood and sod houses, as well as modern accomodation.

Smilla is referring to an igloo built of snow and lined inside with animal skins, which raises the temperature inside up to 20°C.