Prym say:
Fray stop is a colourless liquid that prevents stressed areas; such as button holes, seams, shirt collars, and cuffs; from fraying by reinforcing the fibres. When sewing the edges of curves, Fray Check can be applied to the edge of the curves, which are then conveniently cut before turning and without fraying. This sealing solution gives rolled seams a stable finish. It can even be use to provide a fray-free seal to the edges of self-cut fabric motifs. 22.5 ml of fray stop are included in the dosing bottle with the pipette-like opening. Only after multiple washes can the effect of the fibre-reinforcing liquid can lightly subside. This treatment can be repeated as often as desired.
