The differences between the Flex-Fit and Ergo-Soft earplugs comes down to 3 primary features; material, shape, and sizing. The Flex-Fit earplugs are made from hypo-allergenic silicone, have a straight cone shape, and come in 2 eartip sizes; whereas the Ergo-Soft are made of a soft rubber compound, have an angled cone shape, and come only in size Small.