Trading Card Case: Compartments and Compression
Card cases are not judged on looks. They are judged on whether each compartment is a millimetre too wide or too narrow, and on which edge the lid presses when it closes. The clip shows the lid coming down; it cannot show how thick a hundred cards really are, what half a millimetre of lean does to a divider, or how much compression turns storage into bowing. A square, a feeler gauge and a hygrometer settle all three, and none of these three numbers is a guess; each comes off a test.
01Thirty Millimetres: 100 Cards at 0.3 mm Each
A bare card measures about 0.3 mm, so a hundred stack to roughly 30 mm. That is the starting point, not the compartment size. A sleeve adds 0.05 mm to 0.1 mm per card, another 5 mm to 10 mm across a hundred, and a rigid holder pushes the clear width to 38 mm to 42 mm. Cut pockets to the bare-card figure and a sleeved collection will not go in.
Allow 2 mm of finger clearance as well, enough to pinch the outermost card and draw it out. At zero clearance the stack leans on the wall and corners scuff on every pull. Depth follows the same logic: let cards stand 3 mm to 5 mm proud of the pocket so they can be gripped, because a flush stack means tipping the case and shaking, which is the worst thing for corners.
02Walls at 2.5–3.5 mm: Thin Leans, Thick Eats Cells
Wall thickness belongs between 2.5 mm and 3.5 mm. Under 2.5, the moulding warps as it cools and the pocket becomes a taper, wide at the top and tight at the bottom, so cards jam before they reach the floor. Over 3.5, the same footprint holds fewer cells. Twelve to twenty-four compartments is the usual range, and the more you pack in, the harder even thickness becomes.
Radius the wall-to-floor junction at 0.5 mm to 1 mm. A square joint concentrates stress and cracks from the root on a drop. Making the divider block a removable part beats moulding it into the shell: one cracked cell becomes one replaced panel instead of a scrapped case. The cost is an assembly step and 1 mm to 2 mm of height tolerance to control.
03Lid Compression 1.5–2.5 mm: Hold, Don't Bend
When the lid closes, the insert compresses the stack by 1.5 mm to 2.5 mm, enough to stop it hopping and not enough to create a bending moment. Past 3 mm the middle of the stack is pushed up, and long-term storage produces a bow that does not come out; flatten it and the stress lines on the faces remain.
Compression comes from the lid foam. A 3 mm to 5 mm soft foam compressed 30 to 50 percent lands in the 1.5 mm to 2.5 mm band. Test it by hand: press the closed lid, feel about 1 mm of travel and a spring back, and the setting is right. A hard stop means too much; a gap before contact means too little.
04Divider Squareness ≤0.5 mm: Square and Feeler Gauge
Hold divider squareness to 0.5 mm. Stand a square against the floor plate and try a feeler gauge from the top; if 0.5 mm slips in, the part is out. The usual cause is insufficient draft or uneven cooling, leaving the pocket 0.5 mm wider at the top than the bottom, so cards sit at an angle and the outer one digs a corner into the wall.
Accumulated error across a row is worse. Twelve cells at 0.2 mm each puts the far end 2.4 mm out, and the lid pad no longer lands on cell centres, so it presses crooked. Mould the divider as one piece rather than bonding strips, because glue joints stack error with no way to trim it. After assembly, check diagonals on three panels.
0545–55% RH at 18–24 °C: Climate Window and 30 kg
Card stock is hygroscopic. Above 65 percent relative humidity the fibres swell, flatness goes first, and clamping the stack shut simply traps the moisture inside. Keep storage at 45 to 55 percent RH and 18 °C to 24 °C, where dimensional change is smallest and lid compression stays predictable. Below 30 percent RH the stock turns brittle and corners fur.
Check stacking at 30 kg, roughly three or four cases high. Load the closed lid at its centre with 30 kg for 24 hours, release, and measure residual deflection an hour later; over 2 mm means the ribbing is light. When a case fails this, the fault is rarely the cell walls. It is a lid span too wide with no support in the middle.
| Cell clear width | 30–42 mm |
|---|---|
| Divider wall thickness | 2.5–3.5 mm |
| Cell count | 12–24 |
| Lid compression | 1.5–2.5 mm |
| Divider squareness | ≤0.5 mm |
| Lid stack load | 30 kg / 24 h |
| Storage humidity | 45–55% RH |
| Storage temperature | 18–24 °C |
FAQ
Why design around 0.3 mm per card?
Because 0.3 mm is a typical bare card, so a hundred come to about 30 mm. That is a baseline, not a pocket size. Sleeves add 0.05 mm to 0.1 mm each, which is 5 mm to 10 mm over a hundred, so sleeved storage needs 38 mm to 42 mm of clear width.
Do more compartments always help?
No. Pushing from twelve cells to twenty-four narrows each pocket and thins the walls from 3.5 mm toward 2.5 mm, raising the risk of cooling warp. Size the count to the collection, leave two empty cells as working room, and keep enough finger clearance that cards come out without corner wear.
Does more lid pressure stop bowing?
The opposite. Past 3 mm of compression the middle of the stack is levered upward, and long-term storage bows it. Stay in the 1.5 mm to 2.5 mm band, judged by about 1 mm of spring when you press the closed lid. Bowing is controlled by humidity and load direction, not by clamping harder.
How high can these cases be stacked?
Design for 30 kg on the lid, which is three or four cases. Test by loading the closed lid centre with 30 kg for 24 hours, then measuring residual deflection an hour after release; under 2 mm passes. Beyond that the lid sags, the pad presses into the stack, and you have created the bow you were preventing.