Foil cards and foil badges explained

Foil cards are a shinier, gold-bordered version of a game's normal cards, one foil version for every card in the set. They are a separate drop from the normal cards, considerably rarer, and cannot be crafted from normal cards or mixed into a normal badge.

A foil badge is crafted from a complete foil set, exactly like a normal badge, but it can only be crafted once per game rather than up to five times, and that single craft gives noticeably more XP than one normal craft.

Because foils only drop at a fraction of the rate of normal cards, a foil set is scarcer stock for anyone holding it, which is why foil sets trade and sell for more than the normal version of the same game's cards.