A pale line down the fold, then a split. It happens to expensive folios as often as cheap ones, and the cause is always the same.

What is actually happening

Two stiff boards sit inside the cover, one for each face. If they are butted close together, the cover material has to bridge a hard edge and stretch across it every time the folio is opened.

Materials tolerate bending far better than they tolerate stretching. A PU skin whitens and then splits; a coated fabric goes fluffy; even good hide takes a hard grey crease.

The relief gap

Leave a channel between the boards — a few millimetres of unsupported material — and the cover folds along it instead of stretching over a corner.

It also changes how the folio behaves on a desk. A relieved spine lets the cover fall open and stay open; a butted one springs shut the moment you let go.

Where the stitching goes

A stitch line is a row of holes. Run it down the fold and you have perforated the exact line the material has to flex on.

Beside the fold, it does the same job and none of the damage.

What leather needs on top of that

Hide at full thickness across a spine bulks and resists, so the fold concentrates in one hard line. Skiving — thinning a band of the hide before it is folded — is what lets a leather folio soften with use rather than crease.

Burnished edges rather than raw cut ones are the other half of the same job.