The main body of the TiMags™ are titanium.
There are a few reasons for this:
Firstly, titanium is what we do! (But that alone is not a good reason if I'm being totally honest.)
Secondly, titanium is light ...and so there is no additional weight of, say, steel to reduce effective power of the magnet core.
Thirdly, titanium will not rust ...which is very useful since I know a lot of people will use these in a workshop type environment (including me).