Consisting of the outer nine layers of NASA's current EMU (Extravehicular Mobility Unit - i.e., EVA space suit), the thermal micrometeoroid garment (TMG) performs a threefold function. First of all, it insulates the astronaut, preventing precious body heat from dissipating into space. Secondly, the outermost layer is highly reflective, keeping the sun's radiation from frying the astronaut to a crisp. Finally, the thick layers protect the astronaut from tiny micrometeoroids, which could puncture and depressurize the suit.
After three cooling and ventilation layers, a pressure bladder, and a restraint layer, the TMG begins with a Neoprene-coated nylon ripstop - the innermost, stop-gap layer of micrometeoroid protection. This is followed by seven layers of aluminized Mylar, laminated with Dacron - the insulation here provides most of the thermal protection. Finally, the outermost layer of the TMG is the familiar white Ortho-Fabric covering - made of a blend of Gortex, Kevlar, and Nomex, it can withstand temperatures from -300 to +300° Fahrenheit. This outer covering is the first layer of both meteoroid protection and thermal control (reflection).
Although specific designs may differ between space agencies and governments, every space suit designed for extravehicular activity must incorporate some form of TMG. Described above, of course, is NASA's current version, designed for used on space shuttle missions.