Here is a link showing the exact foam I use in various packages. You should find it in any Pet Store.
The blue foam is about 1/4" thick. Also, if it's running dry (and you've made it correctly) I can only assume that the plug part of the dart is a bit too thick. Just trim it down a bit until it works with the juice you are using. Hope that helps.
(at least until next month) 
The Blue Foam Dart Mod is something I came up with after reading through and trying several similar mods by eclypse and Kristin. Credit should go to eclypse for doing the majority of the research on this. I am only making a slight change to his original idea. This is a bit different in that it uses a stirrer rather than a straw and I promise you that if you try it you will be happy! I use this on a 510 but I'm sure it would work on any cart with a bit of adjusting. I've used the same 2 "darts" for 2 weeks now and have never had a leak or left any juice in the bottom of the cart. Not once! I know how crazy that sounds but just try it!
You will need a stir straw about 2mm in diameter (some I've seen are larger) and some blue aquarium foam.
Cut the stirrer to 12-13 mm. Cut a section of foam to the dimensions shown below. You don't need to be exact as every one I've made works.
Now pinch the 12mm end of the foam and twist it to form a thin area that you will be forcing into one end of the stirrer.
What you should end up with is shown below. Try to force the foam down as far as the arrow shows below.
Now take scissors and trim the end so that the total length is about 22mm.
Fill your cart up (I get about 12-13 drops) and drop the dart in. Use tweezers to straighten everything up. Add a drop or two on top.
You are good to go! The beauty of this is that, for some reason, it runs dry every time and it's very easy to refill. Just pull out the dart, fill and replace it. I've used the same dart at least 20 times.
Enjoy and please let me know if it works for you as well as it does for me.
PS. It works just fine at HV as well!
I'll report back when I've had a little more experience with it.
Thanks and it's a breeze to refill.
Not a bad idea. I'll give it a try although I do vape non-stop and don't have any problem. I do have one size for 3.5v and one (trimmed a bit) for 6v.So I've been using this mod for about 2 weeks now (love it btw). The only problem I've had is wicking when vaping heavily. I tried trimming it down on the sides a bit, but didn't want to take too much off so it wouldn't leak. Just though of an idea tho. I took some scissors and cut a slit down the middle of the foam so there would be a recess for the bridge to rest in a la Eclypse's 2.0 "slug" mod. Seems to be working well so far, no flooding or gurgling. More vapor too
I've had no problems with burning at HV both 5 and 6v using a 510 atty at 2.1ohms so 4.2 should be a walk in the park.
I've tried both. The ZFM seems to always leak for me. You should try them both and see what works for you. I think the ZFM needs to be made just right to work. Maybe I've just not cut it to the correct size. The beauty of the BFD is how simple it is to make and refill.
