Here's what I noticed. The Perlon (blue label) is shiny while the Armor Tough (yellow label which I thought was the same as the old stuff "Doug Hannon") looks kind of chalky. The Perlon also seemed to be more abrasion resistant.

The only other difference is the Perlon is only available in 12 and 15 lb. test while the Armor Tough is available in 12, 14, and 16 lb. test.

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You can't catch tomorrow what you kill today - please practice catch and release.