Mcdavid Hex Chest Protector, Heart-Guard/ Sternum Protection for Baseball & Football, Youth & Adult Sizes Mesh fabric across shoulders back and sides for full-on ventilation hDc Moisture Management Technology is all about the cool and dry Size Based on Chest Size XXSmall : Youth Chest 20-23" XSmall: Youth Chest 23-25" Youth Small: 25-26.5" Youth Medium: 26.5-29.5", Youth Large: 29.5-33", " Youth XLarge: 33-36" Warning: This product is designed to minimize injury from minor impacts to the sternum and chest area. It is not guaranteed to reduce the risk of Commotio Cordis, a rare but sometimes fatal injury arising from sudden impact to the heart.