I asked this question in an email to Columbia. Their response was that the Icon & Icon2 Muscle coverstock is 'particle' but not in the traditional sense. If you compared the particles in a previous TEC series coverstock to the new 'Muscle' coverstock, it would be like comparing a basketball to a pencil tip. It's almost more of an additive than a particle. The Icon2 has less of this 'particle additive' than the original Icon, giving a cleaner look through the heads and a stronger back end reaction. Having thrown both, I will vouch for that. I get a very similar look between my Wicked BRT and the Icon2 (of course, having the same core might have a bit to do with that).