WHOOP sells replacement bands on the WHOOP Store. To replace a WHOOP band, connect the new band’s hook to the clasp of the Strap. Thread the other end of the band through the top of the inner slot of the Strap (i.e. the slot closest to the Strap’s sensor). Feed the band back up through the outer slot so that the end of the band is overlapped on top of itself.
If out of warranty, it costs $120 to replace a full WHOOP unit (strap + sensor), $176 to replace an AUS WHOOP unit, and €100 to replace a EU WHOOP unit, all of which includes a new battery pack.
It costs $30 to replace just the battery pack out of warranty.