Thay also do ladies'.
For the uninitiated (or the non-British) shreddies is a nickname sometimes used for underwear. Apparently it's has military origins.
But these Shreddies aren't your normal underwear. Apparently they help with er, how can I put this delicately, - flatulence.
Gawd knows how they work but there's a hilarious review of them here, where they're called "fart-filtering". I don't know how that filtering works nor where the farts go if they're not allowed to roam free.
According to the manufacturer - "Shreddies flatulence filtering underwear features a ‘Zorflex’ activated carbon back panel that absorbs all flatulence odours. Due to its highly porous nature, the odour vapours become trapped and neutralised by the cloth, which is then reactivated by simply washing the garment."
Yes, very confused. And having second thoughts.