The All Sport Master Mouthguard features anti-concussion firm-fit moulding for unobstructed breathing and clearer speech. Fox 40 has improved the one-size-fits-all All-Sport Master Mouthguard by using softer Dupont Elvax material. The Master still features the same firm-fit moulding that aids in the prevention of concussions, but now provides added comfort and flexibility. Fox 40 Mouthguards are latex-free! One size fits all, with or without strap.