Smith's IO goggles are their flagship models. The IOS has the smallest frame size and is best for smaller faces. The IO is the standard size and is most popular for men. The newer IOX has a large fit that many think just plain looks good. The IO7 is the newest addition to the series and has a redesigned latch to replace lenses. All goggles in the series come with two interchangeable lenses, one for bright days and one for dark.