De vs en

Bonjour Joakim ! I would say that "en" implies that this is the main (and often only) element the thing is made of, whereas "de" would imply that it's one of the elements composing the thing, but there must be more. Colloquially, "en" is used more often than "de". I hope that's helpful! Bonnes Fêtes et à bientôt !