David R. Roisum04.05.18
Bulk is a defining property for many nonwovens. Here we will use the scientific definition as the inverse of density rather than the layman’s usage as a synonym for thickness, which we will get to shortly. In this usage, bulk is measured in volume per mass or cm3/gm in the metric system and in3/lb in the U.S. system. If you increase the bulk, the absorbent capacity increases while the absorbent rate slows. The former is related to pore space volume and the latter to capillarity. The bulkier product is also ‘softer,’ but at the same time more tender and prone to damage, such as during winding as we will see. Finally, bulk costs money in terms of raw materials to make and processing effort to manufacture. Thus, this key measure of bulk relates to many end use properties we care about, namely absorbency, softness, durability, economics and others.
So, how do we measure bulk (as the inverse of density)? You must first measure thickness, which is the layman’s usag
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