The first step in shipping 100 baseball cards is to properly package and protect the cards. You’ll want to get trading card sleeves or toploaders to insert each individual card into. Place the card securely into the sleeve or toploader to prevent shifting or bending during transit. Make sure not to bend the corners or edges of the cards.

Once all 100 cards are individually sleeved or toploaded, it’s time to contain them in the main package that will be shipped. A good option here is to use a rigid baseball card storage box with dividers to keep the rows of cards neatly organized. Make sure the box is exactly the right size, no bigger, to avoid excess empty space where the cards could shift around during handling. Test fit all the cards into the box first before sealing.

An alternative to a storage box is to use rigid paper or cardboard to construct a mailer specifically for these cards. You can cut out several sections approximately the width of a trading card toploader and then tape or glue them together at the edges with sealing tape to form a rigid cardboard mailer. Line the inside with bubble wrap or air pillows for extra protection and dividers again to separate the rows.

Now that the cards are securely packaged in either the storage box or rigid custom mailer, it’s time to add additional outer protection for shipping. The package containing the cards should be placed inside a shipping box at least 2-3 inches larger on all sides to allow for bubble wrap, air pillows or other cushioning material. Make sure to measure and select a box with interior dimensions just slightly larger than the contained package.

Once inside the shipping box, surround the contained package on all six sides with at least 1-2 inches of bubble wrap, air pillows or other impact-absorbing cushioning material. Pay special attention to corners and edges which are vulnerable spots. Additional layers can be added for extra protection depending on the intended distance for shipping and hazards expected in transit like rain or snow.

When filling any empty space left in the shipping box, it’s best to use packing peanuts, air pillows or shredded paper rather than wadded newspaper which can compact unevenly under pressure. Overfill the box slightly so that the lid requires some pressure to close securely without any gaps.

Seal the box thoroughly using packaging tape around all the seams in a H-pattern or overlapping X’s to form a reinforced tape closure. Apply at least 2-3 strips around the entire box perimeter and lid. Make sure no flaps are left untaped where moisture could penetrate. Reinforce especially around corners.

Once the box is fully sealed, it’s time to add appropriate labeling. On the top lid, clearly print the shipping address of where the package needs to go in legible permanent marker or adhesive labels. Include return address as well in case of delivery issues.

In addition to proper address block, add appropriate precautionary handling labels like “Fragile”, “This End Up” arrows, and/or special labels indicating contents are valuable collectibles if shipping via a carrier without automatic insurance coverage. These call out to handlers to take extra care.

Don’t forget to add appropriate postage! For domestic U.S. shipments weighing under a pound, likely cost is around $5-8 depending on speed and delivery tracking options selected. Calculate exact postage cost on your carrier’s website based on weight and dimensions. Be sure to print postage indicia or purchase postage at the post office counter.

For shipping baseball cards, I’d recommend using either USPS Priority Mail which is very affordable for smaller packages under a pound and offers tracking and up to $50 or $100 of automatic insurance coverage depending on added services selected. Or UPS/FedEx Ground which tend to be slightly higher postage cost but also offer tracking. Avoid regular First Class Mail as it offers no protection if package is lost or damaged.

Take the fully packaged, labeled and postage-paid box to your local post office counter during an off-peak time if possible and have the clerks scan it in and apply any special shipping labels needed. Ask for them to carefully handle the package and opt for special services like an adult signature requirement if extremely valuable cards are enclosed.

With the right packaging materials, careful preparation, and proper postage/labeling, your 100 baseball cards should arrive safely at their destination. Just be sure not to overpack so tightly things can shift in transit, but provide ample cushioning so there’s no room for items to bump or rub together during handling in the postal system network. Careful planning and execution leads to stress-free shipping!