It is made from the rarest and finest material woven from the tail fur of the elusive black unicorn, descendent from a 10,000 year blood line. Legend has it the fur has supernatural abilities that enabled Viking kings to conquer mass populations with a single sword stroke.
Disclaimer: Shirt is not bulletproof, fireproof or crash-proof. Also, tests show the wearer cannot necessarily breathe under water, but it does generally let them hold their breath for 2 minutes longer. Please do not try this at home.