Nicky Bigs Novelties M1 Style Army Helmet For Adults This plastic costume helmet is made of thick durable material. The interior will allow the helmet to fit many head sizes. The opening allows up to 62 cm circumference or approximately 24 inches. You can add adhesive back foam in the interior to allow the helmet to fit the smallest of head sizes however we recommend this helmet for ages 12 and up. Size: One Size Fits Most Adults And Some Children Perfect for pretend play, Halloween, Costume Parties, or getting wacky.