Paper Specification
Substrate selection dictates every subsequent production decision.
Weight vs. Caliper vs. Bulk
The most common mistake in paper specification is confusing weight with thickness.
Grammage (GSM)
Grams per Square Meter. The global standard for paper weight. It measures mass, not thickness. A 100gsm uncoated paper will feel significantly thicker than a 100gsm gloss coated paper because the uncoated sheet contains more air (bulk).
Caliper (Mils / Microns)
The actual physical thickness of a single sheet, measured in thousandths of an inch (mils or pts) in the US, or microns (μm) internationally. Crucial for calculating spine widths and ensuring stock fits through press tolerances.
PPI (Pages Per Inch)
A measurement of bulk used in book publishing. It indicates how many pages (not sheets) stack up to one inch. Lower PPI = thicker paper.
Coated vs. Uncoated Surfaces
Coated Papers
Base paper coated with clay and calendared to fill the valleys between cellulose fibers. Forms a smooth, non-porous surface.
- Ink Holdout: Excellent. Ink sits on top, yielding sharp dots and vibrant colors.
- Dot Gain: Low (~15%).
- Drying: Fast, largely through oxidation.
- Finishes: Gloss, Silk, Dull, Matte.
Uncoated Papers
Raw cellulose fibers. Highly porous surface that acts like a sponge.
- Ink Holdout: Poor. Ink absorbs into the sheet, softening edges and dulling colors.
- Dot Gain: High (~22%+).
- Drying: Relies entirely on absorption. Prone to offsetting if stacked too high.
- Finishes: Smooth, Wove, Vellum, Laid.
Grain Direction Rule
Paper fibers align parallel to the direction the paper web traveled through the paper machine. This is the Grain Direction.
Folding against the grain results in cracked fibers, exposing the white core of the paper and ruining the printed image.
Calculate Spine Width