The sheet is in Long Grain if the longer dimension is parallel to grain (MD) direction.

Porosity is a critical factor in Printing Papers, Laminating Paper, Cigarette Paper, Bag Paper etc.

Smoothness is measured by different instruments like Bekk, Bendtsen,Schefield, Gurley, etc.

Changes in dimensions occur with changes in Moisture content.

All papers expand with increased moisture content and contract with decreased moisture content.

For Printing Paper the dimensional change be no greater than 0.25 % in MD and 0.7 % in CD over a humidity range of 20 to 70 %.

Papers require dimensional stability are Printing Paper, Map Papers, Abrasive Papers, Recording Paper, etc.

It is the strength (load) in Kgs that a paper strip of 15 mm width and 150 mm length can withstand before it breaks.

Tensile Strength is important in papers that are printed on Web presses, Bag papers, Wrapping Papers etc.

Stretch is the amount of distortion that paper undergo under tensile stress.

Stretch is important in twist wrapper, cable wrapper, corrugation papers and other similar grades that are folded.

It is the number of Double Folds that a strip of 15 mm wide and 100 mm length can withstand under specified load before it breaks.

Folding endurance is a requirement in Bond, Ledger, Currency, map, Blue Print, Record Papers.

Brightness is the amount of reflectance of blue light at effective wave length of 457 nm.

Brightness test is designed basically to measure the effectiveness of bleaching in removing yellowness.

Spectral reflectance curves of same type of pulps are similar in shape. Hence a reading at a single wave length is sufficient indication of the shape of the curve.

The spectral reflectance curve for an unbleached pulp starts of with a relatively low reflectance in the violet end of the spectrum and raises rapidly to a fairly high value in the extreme red end of the spectrum. Hence unbleached pulp is yellow in color.

Bleaching raises the spectral reflectance curve over the whole range, but the increase is greatest in the blue violet range and less in the red range.

If one were to choose an area of the spectrum in which to take measurements which would best correlate with observable changes in Brightness during the bleaching process, the blue area would be the best choice.

Since the spectral reflectance curves are different for papers of different tints, though they are made with same type of pulps, measurement at a single wave length is not sufficient to indicate the shape of the curve.

Hence Brightness values do not indicate the color /whiteness of the paper.

Whiteness is the amount of reflectance of white light at all wave lengths across the visible spectrum.

Whiteness is a combination of the total reflectance of white light and the
uniformity of the reflectance at all the wave lengths.

A perfect white would have 100 % reflectance at all wave lengths of
visible light.

Most white papers will have a total reflectance of 50-90% with variation at
different wave lengths as high as 20-30%.

All though the whiteness is dependent on both total reflectance and uniformity of reflectance, the uniformity is much more important than the total reflectance.

Whiteness and Yellowness are very subjective quantities which are greatly
dependent upon individual preference

Hence Brightness values do not indicate the color /whiteness of the paper.

All papers have yellow cast, the uniformity of reflectance becomes a measure of yellowness.

If reflectance measurements are made with a green filter and blue filter, the difference between the two readings is a measure of yellowness and the
reading with green filter is a measure of total reflectance.

From the studies of whiteness ratings made visually, it is known that yellowness is about four times as importance as the total reflectance.

Hence, when four times yellowness is subtracted from the reflectance
measured with green filter the result is a measure of whiteness.

Printers Opacity is the most commonly used term.

It is the ratio of diffused reflectance and the reflectance of a single sheet of paper backed by a black body.

Opacity is important in Printing Papers, Book Papers etc.

Indicates the water resistance of a sheet of paper and is expressed as the amount of water absorbed in grams by one square meter of paper in 60 sec.

Cobb test is important in Writing Papers, Printing Papers and in all grades where paper gets into contact with water during its usage.