The resin is the basis of the silly string. It is the plastic component of the string, and is what makes silly string have the physicality that it has. You need to have the right amount of resin to get silly string to work. Too much resin will make the final product too thick, and not enough resin will make it too liquidized, and it won’t be able to form into string. Despite the resin being so important, it only makes up 10 or 15 percent of the total mix.

A surfactant, or surface active agent, is important, as this is what causes the resin to foam and expand–without this, the silly string would not be able to form. The surfactant makes up less than 5 percent of the total mix; so using 3 to 4 percent surfactant will give you the proper amount. Again, you need to have just the right amount of surface active agent. Too little surfactant will make the strands of silly string too sticky, and it wouldn’t come away from surfaces it comes into contact with. Too much of the surface active agent will make the texture too much like a hair mousse or shaving foam, which is not good.

The majority of what goes into the can of silly string is actually propellant, which is what forces the mixture to come out of the can and become silly string. It does this by causing a reaction between the surface active agent and the resin. The contents of your silly string can also be fine-tuned by a few different touches. These include adding a plasticizer, which depending on how much is added, makes the strands of string stronger and less sticky. Silicone liquid will also make the string less sticky and easier to clean up. Adding a flame retardant is important as this will make the mixture safer.