NBSK stands for Northern Bleached Softwood Kraft - the basic wood pulp used in paper and the world standard for the traded commodity. Apart from other paper products derived from it, it's the pulp used in toilet paper and the tissues you use to blow your nose or, if you are a woman, to remove your make-up. That soft feel and the product's strength are due to NBSK's longer fibres.
NBSK's poorer and shorter fibre pulp cousin, BHK - Beech Hardwood Kraft - cannot deliver the qualities consumers have grown to expect. And even NBSK-based tissues are not perfect - the fibres are aligned in the same direction, meaning that the paper can break easily, parallel to the fibres.
According to the authoritative FOEX Indexes, which continues the work started by the Finnish Options Exchange, NBSK costs $1012/ton in the US - slightly less in the important European and Asian regions due to transport costs. And the price has risen 10% in the past two months.
Of course, some of the increase has arisen because pulp mills have been closed by earthquakes in Chile, which normally accounts for 7% of the global total.
But the global recession has led to mill closures across North America and Europe. And the structural shortages are unlikely to end until mothballed mills re-open, and a series of new mills open in China, Brazil and Russia between 2011 and 2014.
Then there are some problems, such as in the US state of Vermont, where mills that depend on recycled paper are suffering as fewer people buy newspapers. Meanwhile, demand for paper products is rising in mass markets such as China and, to a lesser extent, India.
Paper companies that seem best set to get through this period of rising pulp prices are probably integrated ones - the likes of global firms Sappi and Mondi - that have access to their own forests and mills. They are enjoying the revenue benefits of soaring prices for kraft paper used in corrugated cardboard packaging.
But this is not reflected in the two companies' share prices. Sappi is trading at about R30, versus its R140 peak early in 2008 when the economic boom was pushing all markets to new records. Mondi is trading in the region of R45 against its R70 peak in 2008.
In their most recent announcements, both companies' CEOs expressed confidence that the present strength in pulp prices would be sustained for the rest of this year. And though, for now, their predictions have been somewhat overtaken by events, they sounded a note of caution about the effects of Chilean mill re-openings and of new capacity coming on stream over the next few years.
Mondi is planning to curb exports of paper from South Africa and increase those of pulp, whose margins are more attractive.