Paper is the most expensive single item in most small print jobs and the one most often chosen by habit. The specification on a swatch tells you weight, caliper, finish, fibre content and pH, and each of those numbers changes how the sheet behaves at the press and in the binding. Learning to read them takes an afternoon and saves both money and reprints.
The first thing to understand is that paper weight is not a physical property of the sheet. It is a description of a ream, and different paper categories use different ream sizes. That is why 80 lb means two entirely different sheets depending on whether it is called text or cover.
Pounds and grams, and why the numbers do not match
The metric system is simpler: gsm, or grams per square metre, is the mass of one square metre of the sheet. It is an absolute measure and it means the same thing everywhere. The imperial system is a set of conventions: a ream of 500 sheets of a nominal size, which differs between text paper, cover paper, bond and index. Two sheets of identical weight can therefore carry different pound numbers.
| Text (approx.) | Cover (approx.) | gsm | Feels like |
|---|---|---|---|
| 50 lb text | — | 74 gsm | Thin book paper; show-through risk with heavy ink |
| 70 lb text | — | 104 gsm | Standard book and letterhead weight |
| 80 lb text | — | 118 gsm | Comfortable book paper; takes a light impression |
| 100 lb text | 60 lb cover | 148–162 gsm | Stiff text; light card |
| — | 80 lb cover | 216 gsm | Business card weight; takes a firm impression |
| — | 100 lb cover | 270 gsm | Heavy card; score before folding |
| — | 120–130 lb cover | 325–352 gsm | Very heavy cover; a folded card needs a score |
| — | — | 300 gsm cotton | The common letterpress card stock; soft, deep impression |
Cotton papers are usually sold by gsm and described by cotton content — 100 per cent cotton, or 25 per cent cotton with the balance of wood or synthetic fibre. Cotton is prized in letterpress because it is soft, absorbent and takes an impression with a crisp edge and a visible depth. It is also dimensionally restless: a cotton sheet moves more with humidity than a wood-free sheet, which matters when you are printing two colours in separate passes.
Ask for a swatch or buy single sheets and print a test on each before committing to a run. Two hundred sheets of the wrong stock is a far more expensive lesson than four sample sheets.
Caliper, bulk and the hand of the sheet
Caliper is thickness, measured in thousandths of an inch or in microns; bulk is caliper divided by weight, and it describes how puffy a sheet feels for its mass. Two papers of the same 120 gsm can differ in caliper by 30 per cent. A high-bulk sheet feels substantial, folds softly, and is often chosen for books where a thin paper would look mean. A low-bulk, dense sheet feels crisp and prints a harder edge.
Caliper is what you actually need to know for binding. A book block of 200 pages has a spine thickness determined by the caliper of the sheet, not its weight. Measure a stack of 20 sheets and multiply. Guessing from gsm is the commonest reason a finished spine strip is the wrong width.
Coated, uncoated and the impression question
Uncoated stock is the natural choice for letterpress. The surface is open enough to accept ink and compress under the type, which produces the impression people associate with the process. Coated stock — a clay layer on the surface — resists compression, so the impression is shallower and the risk of cracking the coating along the edge of a printed shape is real. Coated paper also dries ink differently, because the ink sits on the surface rather than partly soaking in.
- Uncoated text or cover: best for impression, best for folding, cheapest.
- Coated gloss or silk: sharpest detail, shallowest impression, cracks if folded heavily.
- Cotton or rag: softest impression, most expensive, most responsive to humidity.
- Recycled and wood-free: varies enormously. Test every batch; the surface can change between deliveries.
Pressing type hard into a coated sheet fractures the clay coating at the edge of the image and leaves a halo that cannot be removed. If you must use coated paper, use a light impression and accept a flatter result.
Grain, pH and the things that decide longevity
Grain direction has to be decided at the cutting stage and is covered in detail elsewhere, but it belongs in this list because it is part of choosing stock: a paper that is only available in one grain direction may not be usable for a particular fold. Ask for the grain direction before you order, not after.
pH matters for anything expected to last. Papers described as acid-free or archival are buffered to around pH 7 to 8.5, and they will not yellow or embrittle at the rate of a cheap groundwood sheet. For a book meant to be kept, the difference over twenty years is not subtle. Note that alkaline buffering is not appropriate for every material — some photographic and protein-based materials prefer neutral storage — but for paper and board in a book it is the usual choice.
| Property | Why it matters | What to ask for |
|---|---|---|
| Weight | Stiffness, opacity, postage | gsm, plus the equivalent lb category |
| Caliper | Spine width, fold behaviour | Microns or thousandths of an inch |
| Grain | Folding, warping, spine direction | Grain long or grain short as supplied |
| Finish | Impression depth, ink take | Uncoated, matte, silk or gloss |
| pH | Longevity, yellowing | Acid-free or buffered, with a stated range |
| Sizing | Ink hold-out, feathering | Internal and surface sizing if specified |
Matching stock to the job
Decide the finished object first
A card that will be folded, a book that will be sewn, a poster that will be pinned. Each implies a minimum stiffness and a fold requirement.
Work backwards to weight
A folded card needs enough stiffness to stand: usually 270 gsm and up. A book block wants 80 to 120 gsm so it is not bulky. A poster can go light if it is not handled.
Check the caliper for the binding
If the sheet is going into a case, calculate the spine width from the caliper before ordering the covering material.
Print a test
One sheet, one impression, at the impression depth and ink density you intend. Look at the reverse for show-through and at the fold for cracking.
Show-through is worth a specific mention because it is decided almost entirely by stock choice. Holding a printed sheet up to a window tells you more about opacity than any specification does. A dense 90 gsm sheet can be more opaque than a bulky 100 gsm one, and for a book printed on both sides that difference decides whether the text is comfortable to read.
One more practical note on ordering. Paper is sold in parent sheets, and the finished size you need determines how many pieces you get from each and which way the grain runs. Work out the imposition before ordering, because a parent sheet that yields six finished pieces grain-long may yield only four grain-short, and that difference is a 50 per cent change in paper cost for the same job.
Consider the press as well as the object. A very heavy, hard-surfaced stock resists impression, so it needs more pressure and rewards a press that can deliver it. A soft cotton sheet takes an impression almost too easily and will show every variation in packing. Match the stock to what the press does well rather than to a photograph of someone else's work.
Bring paper into the workshop at least a day before working with it, and keep it flat and off a cold floor. A sheet that has acclimatised will move less after printing, and registration on a second colour will be better.
You can print well on cheap paper. You cannot print well on paper that is the wrong weight for the fold.A printer, on a job that cracked along every crease
Choose the stock before you set the form, because the stock constrains the impression depth, the fold and the binding. A short conversation with the paper merchant at the start of a job is worth more than any amount of adjustment at the press.