Most mouthguards are made from ethylene vinyl acetate, a soft, flexible plastic commonly known as EVA. This single material dominates the market for sports guards, nightguards, and boil-and-bite varieties alike, though the way it’s processed and the thickness of the final product vary widely depending on the purpose. Other materials like acrylic, polycarbonate, and polyurethane show up in specialized or professional-grade guards.
EVA: The Standard Material
EVA is a thermoplastic polymer, meaning it softens when heated and firms up again as it cools. This property is what makes boil-and-bite mouthguards work: you drop them in hot water (the material becomes pliable between 80 and 120°C), press them against your teeth, and the plastic conforms to your bite as it cools. Once set, EVA has strong shock-absorbing qualities. It spreads impact force across a wider area of the dental arch rather than concentrating it on a single tooth, which is exactly what you want during a collision or a grinding episode.
EVA also performs well in the conditions inside your mouth. Research on its mechanical behavior found that the material actually responds better in the presence of saliva and at body temperature, becoming slightly more flexible and improving its energy absorption. That’s unusual for a polymer and one reason it remains the go-to choice decades after its introduction.
Thickness matters more than most people realize. Studies on EVA mouthguards found that shock absorption improves as thickness increases, but the gains level off beyond about 4 mm. That 4 mm mark is considered the sweet spot for sports protection with EVA that has a Shore A Hardness of 80 (a measure of how firm the material is). Thinner guards, like many drugstore options at 1.5 to 2 mm, offer noticeably less protection. Custom guards from a dentist are typically built to hit that optimal range in the areas where impact is most likely.
Other Materials in Specialty Guards
Not every mouthguard is pure EVA. Dentists and manufacturers sometimes use layered designs that combine materials for different purposes.
- Acrylic resin: Rigid acrylic is common in nightguards prescribed for teeth grinding. It doesn’t absorb shock the way EVA does, but its hardness prevents teeth from wearing each other down and can help reposition the jaw. These are the hard, clear splints you might receive from a dentist after a bruxism diagnosis.
- Polycarbonate: This is a tough, impact-resistant plastic sometimes used as a rigid inner layer in laminated sports guards. It adds structural stiffness so the guard holds its shape under repeated heavy hits.
- Polyurethane: Some newer guards use polyurethane blends, which can offer a different balance of flexibility and durability compared to EVA. These show up more often in professionally fabricated guards than in off-the-shelf products.
Laminated mouthguards, the kind made in a dental lab, often sandwich a harder inner layer between softer EVA layers. The rigid core resists deformation while the soft outer layers cushion impact and sit comfortably against your gums and teeth.
Safety and Biocompatibility
Since a mouthguard sits against your oral tissues for hours at a time, the materials need to pass biocompatibility testing. Medical-grade mouthguards sold in the U.S. are evaluated under the ISO 10993 standard, which tests for cell toxicity, skin sensitization, and irritation to oral tissue. Reputable products are free of BPA, phthalates, and natural rubber latex. If you’re buying a guard online or from a pharmacy, look for these specific claims on the packaging. Guards marketed as “BPA-free” and “latex-free” are meeting the baseline safety expectations for something that lives in your mouth.
How Materials Break Down Over Time
EVA doesn’t last forever, and the way it degrades has real consequences for hygiene. A study examining mouthguards used by football players for a single season found dramatic changes in surface texture. New EVA had a smooth surface roughness of about 0.7 micrometers. After one season of use, that roughness jumped to nearly 174 micrometers, a 240-fold increase. That rougher surface creates microscopic nooks where bacteria anchor and multiply.
Cleaning method matters here. Brushing a mouthguard with a toothbrush and toothpaste removed 98% of bacteria, while rinsing with water alone only cleared 60 to 70%. Even with good cleaning habits, the increasing surface roughness over time means older guards harbor more bacteria no matter what you do. For sports guards, replacing them every season is reasonable. For nightguards made of harder acrylic, the timeline is longer, often two to five years depending on how aggressively you grind.
What the Three Types Feel Like
The material a mouthguard is made from shapes how it feels in your mouth and how well it works, but so does the manufacturing method.
Stock mouthguards, the cheapest option, are pre-formed EVA in generic sizes. They’re bulky because they have to approximate a wide range of mouth shapes, and they often require you to clench your jaw to keep them in place. That bulk can make breathing and speaking difficult.
Boil-and-bite guards use the same EVA but in a thinner, more adaptable form. The heat-molding process gives a better fit than stock guards, though the material thins out in some areas during molding, particularly over the biting surfaces where protection matters most. You might start with a 4 mm sheet that ends up closer to 2 mm after stretching over your teeth.
Custom guards, whether EVA-based sports guards or acrylic nightguards, are built from impressions or digital scans of your teeth. The dentist or lab controls exactly where material goes, keeping it thickest in high-impact zones and trimming it where extra bulk would interfere with comfort. The result is a guard that stays put without clenching, protects where it needs to, and feels thin enough that you forget it’s there.