Now, now, not every mobile suit is an uber Gundam machine. Some materials are more common then Gundaniam Alloy. In fact, Gundanium is the rarest alloys in a mobile suit. So I compiled a small list of known materials used in the armor of a mobile suit.
Gundanium - The rarest and most durable metal used in make mobile suits. Machines made with this material are refered to as 'Gundams'. Found mainly on the moon the material is hard to get in large quantities.
Gunduriam - A cheap knock off of Gundanium, Gunduriam offers close to the same protection. Easier to find and access this material is created by fusing Lunar Titanium with other known substances and chemicals.
Titanium - The most common among military mobile suits. Cheap, strudy and reliable Titanium has proven to be one of the best, readily available metals to use in the construction of mobile suits.
Phase Shift - Some mobile suit pilots dont have any access to Gundanium or any of the other strong metals. So they use 'Phase Shift' metal suits. Using generators located inside the suit they activate a thin coating around the body. The coat protects them from most attacks but keep attacking the same spot more than once and their screwed. It doesnt protect from beam sword attacks very well.