Abstract: A device is provided that allows a user to apply a hair treatment chemical to hair. The device comprises an impervious sheet which can be folded along a transverse axis to form an envelope for retaining a lock of hair and a dose of hair treatment chemical. A releasable fastener is arranged around peripheral regions of the sheet to engage the sheet to fasten together opposing portions of the sheet. A region of the fastener engages the device to the lock of hair to retain the device to the hair while the sheet is unfolded, to permit the user to apply a chemical with the device in the open position. The fastener may consist of a layer of grip material comprising a self-engaging three dimensional structure wherein opposing portions of said grip material are capable of releasably fastening together when urged together and of releasably engaging a lock of hair.