Mack's are silicone putty. They work well. In high temps mine will get soft and a bit sticky-so much so that I don't use them over 85 degrees F. Mighty Plugs are beeswax, cotton, and lanolin. Comfortable and do a decent job of blocking noise. With a bit of care they last several weeks. BTW, do not drop the Mack's as most crud will stick to the silicone-ugh. Heros and most every other foam plug provide excellent noise reduction. They do not offer a "high fidelity" cut and some find the muffle effect bothersome. They do, however, offer the highest NR rating and for some that's critical.