TThe Grippi thumb sleeve is impregnated with silicone dots so that you can use it on your line control hand when casting to prevent slippage so that you can throw crisp tight casts withThe Grippi thumb sleeve is impregnated with silicone dots so that you can use it on your line control hand when casting to prevent slippage so that you can throw crisp tight casts without loosing control of slick wet fly line, simple, neat effective!out loosing control of slick wet fly line, simple, neat effective!