Otter Butter is a hand-crafted fly line dressing made in the USA. Originally developed for oiled silk fly lines, Otter Butter can be used on pure silk and synthetic furled leaders and tenkara lines and even modern synthetic fly lines (it does not contain any harmful solvents or ingredients). It comes packed in a plastic container and is a .25 oz. I have been pleasantly surprised at how well "Otter Butter" works. It takes approx. 2 1/2 minutes to apply properly to a CutThroat Thread Furled Leader. Once applied, the leader will float all day long. Never apply Otter Butter to a damp or wet silk line, trapped moisture invites mold. Make sure the butter gets down into the weave and remove excess. An application should last the entire day.