A collection does not usually fail all at once. It fails slowly, in a room nobody thought about, and the owner finds out years later when they go to sell. Almost all of it is preventable and none of the prevention is expensive.
The room decides nearly everything
Four things damage cardboard: moisture, heat, light and physical pressure. Three of those are properties of where the box is, not what it is in. A thousand pounds of holders in a loft will lose to a shoebox in a bedroom cupboard.
The worst places in a normal house are the loft, the garage, the basement and anywhere against an outside wall, because they swing hardest between seasons. The best is an interior cupboard in a room you heat, off the floor.
Humidity, which does the most damage
Paper takes on and gives off moisture with the air around it, and it is that movement that warps a card. Stable matters more than low. Somewhere in the region of 45 to 55 per cent relative humidity is the usual target, and a cheap hygrometer in the box will tell you more than any amount of guessing.
Silica gel helps in a sealed container and does nothing in an open one. If you use it, use enough, in something closed, and dry it out or replace it occasionally, because saturated gel is just a lump.
Light
Ultraviolet fades ink and it does not come back. A card displayed in daylight is being spent, slowly, and the brighter and more direct the light the faster. If you display, use UV-filtering acrylic and keep it off any wall that gets sun. For storage, a closed box solves it entirely and costs nothing.
Pressure and the way things are stacked
Cards stored upright keep their shape. Cards stored flat under the weight of everything above them do not, and a binder stored flat for years will print its page pattern into the cards. Store boxes upright, do not overfill, and put something at the end so the row cannot lean.
Check that nothing rigid is pressing on a corner. A toploader at the end of a box with a bit of room will, over years, dig into whatever is next to it.
The materials to avoid
Old vinyl pages and sleeves containing PVC give off plasticisers as they age, which fog a card surface and eventually attack it. Anything sold for cards today is PVC-free and generally says so. If a page is old, unlabelled and slightly tacky to the touch, replace it rather than finding out.
Rubber bands and ordinary sticky tape both belong nowhere near a collection, for reasons that become obvious the first time you see what they do.
Write it down
The least glamorous and most valuable step. A list of what you have, what you paid and roughly where it is turns a cupboard of boxes into something you or someone else can deal with. Collections are routinely sold for a fraction of their value because nobody could tell what was in them, and that is a documentation failure rather than a storage one.
A ten-year checklist
Interior cupboard, off the floor, room you heat. Boxes upright and not overfilled. Everything sleeved, PVC-free. Nothing in daylight. A hygrometer you glance at twice a year. A list that exists. That is the whole of it, and it will beat almost any amount of money spent on plastic in the wrong room.
Frequently asked questions
What humidity should I store cards at?
Somewhere around 45 to 55 per cent relative humidity, and stable matters more than low. A cheap hygrometer in the box tells you more than guessing.
Is a loft or garage really that bad?
Yes. Both swing hardest between seasons in temperature and humidity, and that movement is what warps cards. An interior cupboard in a heated room is far better.
Why does PVC matter?
Old vinyl pages give off plasticisers as they age, which fog and eventually attack a card surface. Anything sold for cards today is PVC-free and says so.
