The value of a commodity mostly depends on its scarcity, gold and diamonds are intrinsically valuable because they are rather rare, it isn't just a belief like for fiat money. You can't make gold as easily as you can write IOUs.

In this context, I believe Bitcoin is commodity money. It requires work to be created, which enforces a relative scarcity. This doesn't mean its dollar value cannot fluctuate, but I believe it means it can fluctuate less than non-Proof-of-Work cryptocurrencies.