I read in one of the mags (MR?) many moons ago about making my own ground foam. Back then I tried it and it worked very well - I just didn't make enough of it. I wanted to make some more but couldn't find the article. I proceeded anyways since I didn't recall it being anything special.
I made enough ground foam to virtually cover a 4'X8' area solid! For less than $10.
I don't claim to be the inventor of this, but I thought I'd share it since usually I'm asking for information versus sharing information. I do wish I could find the original article because I think it had some tips to use.
Regardless, here's what I did. I went to the Dollar General store and bought 3 packages, at $1 per package, of those smaller, any-color-goes, sponges. Luckily for me each package had all yellow except for 1 and it had 3 purple ones. Each sponge is maybe 3"X5"X1/2" thick. Chinsy things. these particular packages had 9 sponges per package. I also picked up some Tintex - they only had dark green and I knew from doing this before that lighter is better. So I picked up yellow too. By mixing various amounts of the yellow and green you can make different shades.
What I did was tear the sponges into 'bite size pieces' or smaller. this takes some time so tune into your local sports talk show.
I have a blender that I use only for this. Picked it up at a yard sale for a couple bucks. Even if you don't have an extra blender, having the top plastic part is all that really matters. The base/motor can be your good one.
Put 1 or 2 SMALL handfuls of sponge in the blender container. It's better for your blender's motor to error on the light side.
Mix up some Tintex or Ritz dye to the proper proportion in a separate container. Add enough of the watery dye to the sponge (in the blender container) to cover it at least 1/2 of the way. Too much water and the sponge doesn't seem to get chopped up enough, too little and it puts too much of a burden on your blender motor. 1/2 is better than 1/2.
PULSE it about 10 times and then blend on medium speed for 10 - 20 seconds. Dump the stuff into a strainer over a bowl (the bowl will catch the excess dye so that you can use it again for the next batch). Press down lightly on the sponge while it's still in the strainer to get out a bit more excess liquid. LIGHTLY. Dump the dyed sponge onto paper towels to dry. Spread it out with your hand and let it set for several days.
Some of the sponge I didn't dye at all. I thought the purple, mixed in lightly with the green would look nice. I also left some of the yellow undyed for the same reason. Kind of like a dandelion field or something.
The results are not as fine as Woodland Scenics ground foam, but are finer than clump foliage.
I'm telling you - I have so much of this home ground ground foam for $10 and I love it.