The US Postal system is getting a bit more challenging for our snail mail. When packing your cards for a swap / trade the goal is to keep the envelope as flat as possible to reduce chance of damage to your artwork, and to reduce chance of postage due. If cards are not secured together, they tend to bunch up making a bulky envelope.
One result of that bunching - the postal sorting machines catch on the envelope and rip it, resulting in your cards being damaged or lost! This happened in a recent swap I hosted - and is a very sad thing!
Another result if they arrive bunched up is there is Postage Due, which the swap host/partner must pay to receive your cards.
Here are some ways to pack your ATC's for swaps:
1) Using cardboard strips and taping cards to it for stability. (thank you
@Donnacr)
From Donnacr: The strips I use behind my cards are the leftovers after I have cut cereal boxes, etc into ATC backs. I trim them to just shorter than an envelope's width and space my cards along this to spread them out as flat as I can.
2) Overlapping ATCs and using washi / painters tape
on both sides to secure cards together.
3) Using part of a 9 pocket trading card holder for cards.
I include a host card, and put the thinnest 2 cards back to back in one slot. I put address label and stamps in an ATC sleeve and slip in behind a single card.
I mail this in a business sized envelope. If I'm including a Self Addressed Stamped Envelope (SASE) I fold the return envelope in thirds and "wrap" around the 3 card strip.
If using a greeting card sized envelope to mail the swap cards - I fold the business sized SASE in half and put the taped cards in the folded area. That gives your cards some extra protection.
Feel free to ask questions or share your own tips!