Low-priced stock that sells at less than $1.00 per share. Often highly-speculative and volatile, such as start-up mining companies. While, in general, penny stock are considered high-risk securities, some penny stock mature into less-speculative investments. All penny stock are traded over-the-counter.
In its natural form, cork is also a very good fire retardant, although cork dust is actually extremely flammable (because here the cell structure has been broken down). Impermeable: Cork has a magic chemical in its cell membrane that makes it completely impermeable to liquids and gases.
It's not like everyone knew the derivation of the word, so the change probably made sense. However, confusion persists today regarding which word to use. Flammable is the modern term for a material that catches fire readily. Inflammable means the same thing. If a material won't burn easily, you could say it is not flammable or nonflammable.