All Icons are 2618 aluminum. It's easy to find on their website.

The old TRWs and the Speed Pros are all their version of 4032.

Most of the high end piston manufacturers who have two lines of pistons make the lower priced line out of 4032 and the higher priced line from 2618.

4032 has a much higher percentage of SILICON. Like sand. Silicone is what's in breast implants and silicone RTV.

The higher silicon content of 4032 makes it expand less with heat so can be used with tighter piston to wall clearances. That makes it more applicable to street engines which have a large number of cold starts.

R.