This stuff has been around since Hardy started printing catalogs! Ahh... the classic English Floatant. Available with silicone (green) , Mucilin is denser than most other formulas, which makes applying it less messy when you are coating a fly or your leader.
Another good product for greasing your line, leader or tippet to get it to float.
It has a loyal following of anglers around the world and still remains as one of the best in the business after all these years.