In a future with space magic, fusion powered rifles, hover bikes, overgrown smurf people, and dinkle-bots...what you question is how beards would work with helmets. These helmets you speak of are infused with space age testosterone powered circuitry that was the last great military achievement of mankind before the collapse. They are snag proof and tight fitting and also feature an artificial intelligence feminine voiced program that complements guardians on their fighting prowess and beards regularly to boost guardian morale.