Björn Borg Core Original Loose Boxer. Björn Borg Core Original Loose Boxer is a boxer brief with a retro design. It is slightly airy and has a more loose fit. These underpants are made of cotton and elastane and are comfortable to wear. As an extra nice detail, the underpants have a faux fly and the waist is adorned with the Björn Borg logo. The waist of the underpants is nicely stretchy thanks to the elastic band. Björn Borg Core Original Loose Boxer is a great addition to your underwear collection!