I would google this except I can't figure out what it would be called. I need more multisensory things for letter formation as one of my little students is strangely resistant to the carpet board. I was thinking of making something I've seen others do, which is putting hair conditioner or gel into a large ziploc bag such that when you make letters on it with your finger, it leaves a line behind. I suppose it would be easy enough to play around until I figure out what works, but if someone has a formula already, I'll follow. I wonder if there's anything I could put in that would give a nice swirly effect... not food coloring, that would just turn into brown smush quickly enough.
Hair gels works great - just get the air out of the bag and seal it with tape. You can add glitter if you want. You can also use a couple of different types of paint so they combine them. I think they are often called sensory bags.
So glad to see sensory bags up for discussion! I love to use those bags on a piece of paper, or better yet a placemat, in a color that really contrasts. Not a little contrast......a lot of contrast. Helps you to see the lines you have made. Salt trays (which can be filled with sand, or I even saw Tang once) they hold a line and are not the same feel as carpet. Shaving cream? Kinda messy...but a lot of fun! For making letters first squish it onto the table in just a skiff then write. The billowing fluffs are fun but don't show a line well. Again, use a tray and that would help the mess, but this one is just messy all around.....so maybe it won't work for you.
multisensory practice I have the students use the palm of their hands. We call it a palm pilot. They use one finger and the palm of the other hand to practice writing letters. Die cut sandpaper letters. Using a partners back is fun with lots of giggles. Chalk on dark paper. ABC macaroni.Scrabble tiles.
In August of 2009, I mixed some tempera paint in an icing container to get a custom color. I put the lid on when I finished and it just kind of got stuffed in my supply cabinet. Considering the lack of amazing seal, I was surprised to find it still perfect a few weeks ago. So I think with a quality locking bag and enough paint inside, it should be fine for quite a while. I figure the kids will ruin it before the paint gets crummy. I liked using a q-tip as shown on that site. Seems to make a more defined shape.