(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.
Urea-formaldehyde, also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a non-transparent thermosetting resin or plastic. It is produced from urea and formaldehyde. These resins are used in adhesives, finishes, particle board, MDF, and molded objects. UF and related amino resins are a class of thermosetting resins of which urea-formaldehyde resins make up 80% produced globally. Examples of amino resins use include in automobile tires to improve the bonding of rubber to tire cord, in paper for improving tear strength, in molding electrical devices, jar caps, etc.