In this instructable I'll show you how to make expanding foam using Gorilla Glue and flour.
Step 1: Ingredients
Choose your ingredients. There are only two - glue and flour.
The glue must be a polyurethane glue, such as Gorilla Glue. It's the polyurethane that has the foaming reaction.
Flour - any flour will do - plain flour, corn flour (AKA cornstarch).* In fact, any fine powder should work.
*Cornflour is called cornstarch in the United States and Canada, and cornflour in the United Kingdom, Ireland, Israel and some Commonwealth countries. In the United States and Canada cornflour refers to cornmeal that is very finely milled.
Step 2: Mix
Wear rubber gloves.
Simply mix the two ingredients together. I used a ratio of 1:1, but it's not critical. Be aware that the mixture will expand by about ten times, so factor that in when preparing. If you use it for filling holes, it's probably going to overflow, and get over everything. When wet it is very sticky.
The mixture will expand to its full extent in about half an hour, but will take another hour or so before it is fully cured.
Step 3: Variations
Once cured, the foam is quite rigid. If you want a softer mixture, add a little water to the flour before adding the glue. Make a paste with the flour/water mix, then add the glue.
You can also add colour to the mix; any water based colour should work. Acrylic paint, ink, watercolour.
Step 4: That's It.
Here's a video I made about Gorilla Glue Foam. I hope you find it, and this instructable, informative.