Preventing heat escape through insulation called "aerogel"

The rover is also kept warm by a special layer of insulation, called solid silica aerogel, which prevents heat from escaping outside of the rover body walls. Aerogel traps heat inside the rover body. It is a unique silicon-based substance nicknamed "solid smoke" because it is 99.8% air. Aerogel is one thousand times less dense than glass, so it is extraordinarily lightweight, which makes it much cheaper and easier to launch and fly to Mars.

Aerogel is a powerful material. Not only can it block heat from leaving the Mars Exploration Rover body, but it´s the same material used to trap "cosmic bullets" for the Stardust spacecraft that will fly through a comet¹s tail in January of 2004, just as the rovers are reaching Mars.