Silly Putty

I keep some silly putty in my backpack as something to keep my hands busy when I am doing work at the library. Silly putty is obviously very stretchy, but when you pull hard enough it breaks. I was able to find the Young's modulus of silly putty online for rapid deformation (1.7 x 10^6 N/m^2) and I want to use that information to see how much force it takes to make silly putty break (ultimate strength for tension). I did a mini experiment in which I preformed 10 trails of stretching the silly putty quickly and roughly finding at what ∆L the putty broke. I approximated this at 10 cm, with a Lo of 3 cm. Using the equation F/A= E * (∆L/Lo) I can find my experimental tensile ultimate strength for my silly putty, which I calculated to be 5.7 x 10^6 N/m^2 when rapidly stretching.