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The thickness or 'calliper' of paper, board and tissue can be measured on a single ply or multiple plies using a deadweight micrometer and quoted in μm or 'microns'. The micrometer used in determining tissue thickness has a lower foot pressure. Bulking thickness is the thickness of a single sheet calculated from the thickness of several sheets.
Smithers is UKAS, ISO 17025 accredited for thickness and bulk thickness testing of paper to British standard BS EN ISO 534 and International standard ISO 534. Paper thickness testing is included in Smithers' Paper Proficiency Service.
The thickness of tissue is measured in accordance with British Standard BS 7387 and BS EN 12625-3 using a Messmer instrument. The thickness of corrugated board is measured in accordance with British Standard BS 4817 using a Buchel van der Korput instrument.
Compressibility index is calculated from the grammage and bulking thickness of the paper sheet. Compressibility index is determined by Smithers in accordance with British Standard BS 7387 and is expressed in µm.
Apparent sheet and bulk density is calculated from the corresponding thickness and grammage determinations.