(hint #1) Being able to play whatever I want has been a central theme to my own discovering how to play guitar. I've been on that path for 37 years, and it's enabled me to uncover, test and refine a unique, skill generating learning approach.
It is important to note that urethane foam is most commonly used to refer to a material made from polyurethane. The urethane reference in this name is to the type of links, also known as carbamates, that join the units in polyurethane.
There is some potential for confusion as the word urethane on its own is often used for a specific carbamate also called ethyl carbamate, but despite the name, this substance does not appear in the foam. Perhaps the best known use of urethane foam is in bedding, such as mattresses. Because it is artificial, the foam can be made to a particular density, meaning manufacturers can offer a range of mattresses with different degrees of softness or firmness and even produce a mattress to order.