Silly Putty was invented during the second world war by Chemists who were concerned about the rubber supply began researching synthetic replacements. They stuck upon a stretchable, solid liquid material sure it was of no use at all in the war effort… but it was sold as a novelty toy inside plastic eggs. They benefited from a report in the New Yorker and as a result an order for 250,000 was asked for!
The silicone polymers used allow it to bounce and be manipulated but if you were to strike it with a hammer it will break. Its liquid silicone internal makes it act as a liquid over a long time and if you left it long enough it would form a puddle, it is a solid over a short term.