Silly String was originally designed to be a spray on cast for broken bones

When Fish and Cox, two inventors, first created the compound that would eventually come to be known as Silly String, they had a very different plan in mind. They wanted to use the substance, which when sprayed from a can would quickly harden, as a form of instant cast. Simply spray it on a broken arm or leg and it would quickly set into a hard and immobile cast. When this did not work, they used it instead as a children’s toy, and it quickly became famous.