The Dye i4 has to be one of the most popular goggles ever produced! These are very lightweight, have a quick-change lens, and fit very comfortably! The i4 Pro utilizes the best of the i4 and the i5 by adding the goggle strap from the i5 which uses a ratchet style strap to tighten, which includes a pad for additional protection on the back of your head.