The most important thing when fixing bent baseball cards is to be patient and go slow. Rushing the process can easily damage cards further so it’s best to take your time. There are a few different methods you can use depending on the severity of the bend:

For minor bends, your best option is to use heat and weight. Place the bent card directly on a heat source like a clothes iron set to the lowest possible heat setting, usually linen or synthetic. Make sure to lay a thin cloth like a towel or parchment paper over the card for protection. Apply very light pressure with the iron for 10-15 seconds, checking regularly, then remove from heat. Immediately place several heavy books on top of the card to flatten it out while it cools. Leave books in place for at least 12 hours.

For more severely creased cards, you may need to incorporate moisture along with heat and weight. Dampen the creased area very lightly with a damp paper towel or cloth by dabbing, not soaking. Too much moisture can damage the card. Place the dampened card on a flat surface and use the iron method as above, being extra careful to not push too hard with the iron near the crease. Leaving weights on the card overnight allows the moisture to gradually relax the fibers in the cardboard back into position as it dries.

Another technique for stubborn creases combines heat, moisture and mechanical action. Very carefully use pure grain alcohol (not rubbing alcohol which can damage the surface) and a cotton swab or cloth to dampen just the creased area. Apply gentle but steady pressure with your fingers to work the fibers back flat while heating with an iron set to low. Or place a couple heavy books on top to add weight and let dry completely before checking progress. Repeating the dampening and flattening process a few times may be needed for severe cases.

For truly mangled cards beyond repair with the above methods, your last resort is trimming or cutting. This should only be attempted as a final solution if the card is otherwise uncollectible due to heavy creasing or folds. Carefully and precisely trim or cut away just the most damaged portion of the cardboard back using a very sharp hobby knife or scissors. Take your time to get a clean cut. The front of the card can then lay flatter, though it will have a slight trimmed edge. Handle carefully from then on to avoid further damage.

Proper storage is key to prevent baseball cards from bending again after repair. Store in semi-rigid plastic pages, top loaders or magnetic holders. Boxes are preferable to long term storage compared to loose piles which can slip and slide against each other. Opt for acid-free paper or poly sleeves and pages if possible. Maintain cards in a temperature controlled environment away from direct heat or humidity which can cause warping over time. With patience and care, many damaged cards can be restored close to their original condition using heat, moisture, weight and sometimes precision trimming. Always go slowly and carefully for the best results.