Which iconic toy was invented while trying to create synthetic rubber?

Silly Putty’s origin story begins with an accidental discovery during the rubber shortage during World War II. During WWII, many of the countries that produced rubber were being invaded at the time. Because of this, the Allies faced an extreme rubber shortage. In an effort to combat the lack of this essential manufacturing item, the U.S. government contracted companies to create a synthetic rubber substitute that could be made from readily-available materials. It was during this experimental process that one of the world’s most popular toys was inadvertently created.

Source: Custom Powder