Short answer: use a standard #10 window envelope (4 1/8" x 9 1/2"). Lay the slip face up, fold the bottom third up, then fold the top third down over it: a letter fold, also called a C-fold. Slide it in with the address side toward the window, then check that the whole address and the whole barcode show through the window before you seal.
Why the fold matters now
TCGplayer's tracked packing slip carries a USPS Intelligent Mail barcode (IMb) for eligible orders of $49.99 or less. The slip itself becomes the address: TCGplayer calls the window envelope "a standard #10 envelope with a clear window that displays the buyer's mailing address and USPS tracking barcode", and says that when you fold and insert the slip, "both the address and barcode should be visible through the window." If the barcode is hidden, USPS can't scan it, and the envelope gets no tracking. How the feature works and who qualifies: TCGplayer free envelope tracking.
The letter fold, step by step
These are TCGplayer's steps from its help article How Does Envelope Tracking Work for My TCGplayer Orders? (checked November 2, 2026):
Lay the packing slip flat. "Place it face-up with the top of the page closest to you."
Fold the bottom third up. "Bring the bottom edge of the paper up approximately one-third of the way."
Fold the top third down. "Fold the top of the page down over the first fold to create a standard letter fold (also called a C-fold)."
Insert the packing slip. Put it in the window envelope "with the buyer's mailing address and barcode facing the window."
Check the window. "Before sealing the envelope, make sure the full mailing address and tracking barcode are clearly visible through the window and aren't covered or cut off."
Our tip: depending on which way each third folds, the printed address can end up facing in, toward the rest of the slip. Before you insert it, hold the folded slip and look: if you can't see the address on an outside panel, unfold and fold the top third the other way so the printed side faces out.
Above or below the address? Check both
TCGplayer's help text says the tracked slip "includes a USPS Intelligent Mail barcode (IMb) printed below the buyer's mailing address." The sample slip pictured in the same article shows the barcode above the buyer's name, with a dashed "Fold Line" printed just under the address block. Your slip may differ from either.
So don't fold to a memory of where the barcode goes. Fold, insert, and look through the window: the full address and the full barcode both have to show, with nothing cut off at the window's edge. If one of them is hidden, take the slip out and adjust the fold. TCGplayer: "If the address or barcode isn't fully visible, adjust the packing slip before mailing. An obscured barcode may prevent USPS from scanning and tracking your envelope."
The envelope
- Size: TCGplayer says "Use a standard #10 windowed envelope (4 1/8" x 9 1/2")" and that "Larger or smaller windowed envelopes may not align the address and barcode with the window correctly."
- Window only: "Do not use a tracked packing slip with a regular (non-windowed) envelope, as the tracking barcode must be visible for USPS sorting equipment to scan it."
- Nothing over the barcode: TCGplayer lists "tape, stickers, or labels over the barcode" among the things that stop a scan.
- Postage: still yours. TCGplayer: "Your envelope ships with a standard First-Class stamp, exactly as before." How many stamps a card envelope needs: stamps for a trading card.
- Out of window envelopes? TCGplayer says to print the standard, non-tracked packing slip instead, so you still ship within the 48-hour window.
Print it right before you fold
A good fold can't save a bad print. TCGplayer's printing rules for the tracked slip: a standard 8.5" x 11" sheet, a laser or inkjet printer "set to at least 300 dpi", and "Print at 100% (actual size)", because "Scaling the page will distort the barcode and prevent USPS scanners from reading it." After printing, check that "the barcode bars are sharp and evenly spaced with no blurring or smearing." If slips still don't scan, see tracked packing slip not scanning.
Which orders get a tracked slip
TCGplayer's help article: "Orders totaling $49.99 or less from an individual seller with a USPS-verified domestic U.S. shipping address are eligible for envelope tracking." Orders over $49.99 still need a real tracked shipping label: TCGplayer recommends tracking over $20, requires it over $49.99 and requires signature confirmation over $250. Sorting a batch: tracked slip or shipping label?
FAQ
How do you fold a TCGplayer packing slip for a window envelope?
Lay the slip face up with the top of the page closest to you, fold the bottom third up, then fold the top third down over it. That is a standard letter fold (C-fold). Put it in a #10 window envelope with the address and barcode facing the window.
What size window envelope does TCGplayer's tracked packing slip need?
TCGplayer says to use a standard #10 windowed envelope, 4 1/8" x 9 1/2". It warns that larger or smaller windowed envelopes may not line up the address and barcode with the window.
Is the barcode above or below the address?
TCGplayer's help text says the Intelligent Mail barcode is printed below the buyer's address, but the sample slip in the same article shows it above the address. Don't rely on either: check that the whole address and the whole barcode show through the window before you seal.
What if the barcode is cut off by the window?
Take the slip out and refold it so both the address and barcode sit fully inside the window. TCGplayer says an obscured barcode may prevent USPS from scanning and tracking the envelope. Don't cover it with tape or stickers.
Can I use a plain envelope with a tracked packing slip?
No. TCGplayer says not to use a tracked packing slip with a non-windowed envelope. If you run out of window envelopes, print the standard packing slip instead and ship on time.
Sources
- TCGplayer Help: How Does Envelope Tracking Work for My TCGplayer Orders? (checked November 2, 2026)
- TCGplayer Help: How should I ship my TCGplayer orders? (checked November 2, 2026)