Foam, polyfill, or any other product works well only if you use the right size piece in the cart. Too tight and you get weak
juice transfer to the atty bridge. Too loose and you get leaks. The key is to find just the right size. I have found that a loose fit that slips easily into the cart works best. When you add the
juice it expands just a little and works just right.
Experimentation is necessary. Personally, I'm liking the Ego
tank for my primary vape and a 306 atty with a drip tip for an alternate.