12 packs per box, 15 cards per pack.

Collector Boosters are turbocharged booster packs loaded with delicacies for collectors and anyone who wants to style out their deck.
Pack Contents:
15 cards from Throne of Eldraine:
1 rare/mythic rare with extended art.
1 foil rare/mythic rare.
9 foil commons/uncommons.
3 special frame cards (borderless planeswalkers or "showcase" cards).
1 ancillary card (non-foil version of any ELD card otherwise not found in traditional ELD boosters, such as the Buy-a-Box promo.
1 foil token.