When should I throw away a microfiber towel?

Retire a towel when it becomes stiff, loses absorbency, has hardened residue such as cured coating or compound that does not wash out, or has been dropped on the ground and may hold grit. Towels can be downgraded rather than discarded, for example from paint use to wheels, door jambs or engine bays. A towel that has picked up grit should never return to paint duty.