The selection of paper pulps and their subsequent refining influence formation to a great extent. Short fibers will form better than long ones, while long fibers, which give strength in terms of folding endurance and tear resistance, when used in preponderance, tend to give a cloudy or bunchy look to the formation of the sheet. Loading or fillers improve formation, permitting closer packing and greater density in the sheet, thus improving both levelness and LOOK-THROUGH . There are limits, however, to the amount of loading than can be used, as it weakens the paper because it is dead weight and contributes no strength on its own. (17 , 72 , 143 )
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