Most leather notebook covers are cut from hide around 1.0–1.5 mm. It is cheaper, it folds easily, it photographs softly. And it collapses the moment you take the notebook off a table.
That is the whole case for cutting thicker, and it is a practical case rather than a luxury one.
What thin leather does
A thin cover has no structure of its own, so it takes the shape of what is inside it. Hold it in one hand and the panel bends under the pen; the page moves as you write. You end up needing a surface, which defeats the point of carrying a notebook.
It also curls at the corners inside a bag, because there is nothing to resist the fold.
What we cut
Buttero at 2.2–2.4 mm, Pueblo at 2.0–2.2 mm. Both are firm enough that the cover stands on a desk instead of slumping around the block, and firm enough to write on held in one hand.
The trifold adds a third panel over the fore-edge — 70 mm on A6, 100 mm on A5 — and a firm trifold behaves differently from a soft one: it holds the wrap shape instead of relaxing into a curl.
The cost of it
Two things. A thick cover is stiff for the first fortnight, and it loosens only where it folds — the panels stay firm for the life of the cover, which is the point. And it is heavier: not enough to notice in a bag, enough to notice in a coat pocket at A6.
If what you want is the thinnest, lightest possible wrap, we are not the right workshop. If you want to write standing in a corridor, this is the reason to buy one.
Where thickness does not help
It does not make a cover more protective in a bag — the shape does that, which is what the trifold flap is for. It does not make the leather last longer; an uncoated veg-tan hide at 1.2 mm will outlive most of what is in your bag too. And it does not improve how a cover ages: patina is about the surface and the tanning, not the substance under it.
Thickness buys you one thing, and it is the flat page under your hand.
How to check before you buy anything
Whoever you buy from, ask for the thickness in millimetres. It is a number every workshop knows and most product pages leave out, and it tells you more about how a cover will behave than any photograph will.