Choosing Paper and Cover Weight for Saddle Stitch
Which paper properties matter besides weight?
Grain direction is the first, because paper folds cleanly along the grain and cracks across it. A sheet whose grain runs the wrong way relative to the spine produces a rough fold and, on heavier stock, visible fibre breakage that no amount of pressure improves.
Opacity is the second, and it is what stops the reverse of a sheet showing through on a light stock. It does not track weight exactly, since a bulky uncoated sheet and a dense coated one of the same weight can differ noticeably in how much they show through.
Bulk is the third and the one most often confused with weight. Two sheets of identical grammage can occupy different thicknesses depending on how the paper is made, which is why the specification worth asking for is caliper rather than weight alone.
How does stock affect creep?
Directly, because creep compensation is derived from caliper. The total shift is the number of nested sheets multiplied by the thickness of each, so a heavier sheet produces more creep at the same page count and needs more compensation.
The failure mode worth knowing is a stock change made after imposition. Switching between coated and uncoated stock alters caliper materially even at the same nominal weight, and the compensation calculated for the original specification is then wrong. Re-check whenever the paper changes, not only when the page count does.
Does the cover need a different weight?
Not necessarily. A self-cover booklet prints the cover on the same stock as the text, which is cheaper and entirely appropriate for short, light booklets such as programmes and newsletters. The cover is simply the outermost sheet of the nested set.
A heavier separate cover earns its cost when the booklet will be handled repeatedly or needs to feel substantial, and becomes more attractive as the page count grows, since a thick text block on light stock is where a self cover starts to feel flimsy. The heavier sheet also adds thickness at the spine, which feeds back into the creep calculation.
What should I check before committing?
Ask for a physical dummy in the actual stock. A folded, stapled and trimmed sample answers questions about spine bulk, whether the booklet stays closed and how the face edge looks after trimming, none of which are apparent from a specification sheet.
Confirm the stock before imposition rather than after, because the creep allowance depends on it. A late change to a heavier or differently finished sheet means the imposition has to be regenerated, and a job printed with stale compensation shows uneven margins that cannot be corrected once trimmed.
| Change | Effect on spine | Effect on creep |
|---|---|---|
| Heavier text stock | Thickens faster | More compensation needed |
| More pages, same stock | Thickens proportionally | More compensation needed |
| Coated to uncoated | Caliper changes | Recalculate before printing |
| Separate heavy cover | Adds spine thickness | Include in the calculation |
| Self cover | No extra thickness | Cover creeps with the stack |
Common questions
Why do page limits differ so much between printers?
Because the limit is really about spine thickness, and a page count means nothing without the stock attached. A figure quoted for light text paper will not hold for a heavier sheet, so two printers can give very different numbers while applying exactly the same physical constraint.
Does changing paper mean re-imposing?
If creep compensation was applied, yes. The allowance is calculated from caliper, so a different stock makes the existing compensation wrong. Coated and uncoated sheets of the same nominal weight can differ enough to matter, so the check is worth doing on any stock change.
Is a heavier cover always better?
No. It adds cost and spine thickness, and for a short, light booklet it can be unnecessary. Self covers are entirely appropriate for programmes, newsletters and similar work; a separate cover earns its place when the booklet is handled repeatedly or the page count is high.
Can I judge stock from a specification sheet?
Only partly. Weight and caliper tell you how the stack will build, but how the booklet feels, whether it stays closed and how the trimmed face edge looks are best judged from a physical dummy folded and stapled in the actual stock.
What happens if I ignore creep on heavy stock?
The inner pages project furthest and lose the most in the face trim, so margins that were equal in the file come back visibly uneven in the booklet. It cannot be corrected after trimming, which is why the allowance is decided at imposition.