Its tough to know because Brunswick has about 50 different names for coverstocks, and I would guess that many are just different names for the same shell. Original Inferno had Activator shell which replaced PK 18 as the strongest from Brunswick. However, what made Activator strong was the shell prep which featured the rough buff finish. Basically it was about an 800 grit with polish on top. Also, the low rg symmetrical core matched up very well with the pearl activator. Probably the most popular and versatile ball of that era from Brunswick was actually the Vapor Zone which featured Activator+ ( not sure how it differed from Activator ) and a low rg asymmetrical core.