When purchasing card sleeves, it's important to make sure that you get the right size for your cards. There are different sizes available, and you'll need to ensure that your cards will fit snugly and securely in the sleeves you choose. You should also consider the thickness of the sleeves, as some sleeves are thicker than others and may provide more protection. You may also want to consider the material of the sleeves, some sleeves are made with acid-free and PVC-free material which is great for the longevity of the cards, specially for collectible cards.