Bulk
Also: bulk, specific volume
The volume per unit mass of a paper, calculated as caliper divided by grammage, reported in cm³/g.
Bulk is the inverse of density. A high-bulk paper takes up more space per gram, which is useful for book paper (thick-feeling book at low weight) and for corrugated fluting (stiffness per gram). Low-bulk papers pack more mass into less volume, useful for bible paper and high-stiffness cover stock.
Formula: bulk (cm³/g) = caliper (microns) / grammage (g/m²) / 1000. A 1-micron-per-gram paper is very dense; 2 microns per gram is bulky. Furnish, refining, and calendering all influence final bulk.
Related
- Calendering. A finishing step where the sheet passes through pressurized roll nips to smooth the surface and control caliper.