A tried and tested line floatant that has been around for years and is still one of the best available.
 
Silicon Mucilin Floatant Paste is a blend of silicon and mucilin which makes a highly efficient water repellent, which in turn helps your flyline or leader float.  The difference between Mucilin 'Green' and Mucilin 'Red' is the added silicon which gives the 'green' the advantage of improving a lines floating ability even more.
 
This floatant grease paste comes in a handy re-sealable tub and a felt pad to apply it to the line.
 
Please note, this floatant is only suitable on plastic coated lines, mono and flurocarbon and should not be used on silk fly lines