Mitchell - It is an aluminum alloy frame, the same as many top manufacturers use today. You find them everywhere in the quality handgun arena. And they are holding up just fine. The real plus is being able to shed a few ounces, which can make a substantial difference in a long range session, or carrying all day, as well as being more corrosion resistant than carbon steel. Today's alloy gun frames are great.

it is a alloy frame like all the classic (metal) sigs