What’s Inside Silly String: The Secret’s in the Solvent
For a real laugh, look no further than the original patent applications of your favorite old-school novelty products. Take Silly String. You know it as the bane of every high school principal’s existence come Halloween. Way back in 1972, inventors Robert Cox and Leonard Fish characterized it as “a pressurized or ‘aerosol’ can containing a composition of matter for producing a string of plastic foam.” “Such a combination,” they continued, “has substantial play and decorative utility.” Because you can’t say “ultimate spiderweb war weapon” in a patent, apparently.
Despite its name, Silly String is very serious about keeping its recipe under wraps. Originally sold by Wham-O, the trademark was acquired by the Car-Freshner Corporation in 2001. The string’s secret is in its solvent and its surfactant, neither of which the company will name—along with other stuff it won’t confirm. Surfactant is just a fancy name for detergent, which is amphiphilic—both hydrophobic (water repelling) and hydrophilic (water attracting). That attraction-repulsion combination helps glue together molecules in the solution so the string comes out in one solid, silly stream. The stickiness also helps the stuff lightly cling to surfaces—and people—after launch.
Deionized Water, Solvent
Shaking the can mixes the solvent-that-shall-not-be-named with the rest of the ingredients, forming a temporary blend of plastics, minerals, and propellants. Both the water and the solvent quickly evaporate outside the can, leaving the foamy solids behind.
The aerosol powerhouse that sends the mixture flying is a relative of Freon-12, the ozone-depleting refrigerant that pressurized first-gen Silly String back in 1972. Inside the can, this propellant is in a compressed liquid form; when you hit the nozzle to rain silliness upon your enemies, the pressure drop causes the liquid to boil and vaporize, expanding and pushing the goo out of the can.
The string gets its structure from this durable polymerized plastic. Mixed into the can as a powder, it creates a viscous solution. But once the plastic is propelled into the air, it forms a sturdy exoskeleton. The shell will stay in place for weeks if you never quite get around to tying up the loose ends of your Fright Night festivities.
Without talc, the string would be all plastic skin and no body, like a joke that falls flat. Made up of mostly magnesium, silicon, and oxygen, this absorbent mineral gives the resin substance, filling out the string as it expands to the size of the can’s nozzle.
Isopropyl Alcohol, Ammonia
These two ingredients help keep the solution stable so it can last between Halloweens. The alcohol prevents bugs from growing inside the can. The ammonia—or other basic compound—raises the pH enough so the can’s metal interior won’t corrode. After all, nothing is less silly than rusty Silly String.
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