Part of Metal Type’s Printing Advice section, here Phil discusses Bristol Board.
Bristol Board was the generic name for card stock that ranged in weight from 180 pounds for 1000 sheets of 22 x 28 inches to pretty much double that in thickness. The thickness for 180M was just under 10 mils or thous. of an inch.
Posting or Writing Grade
This card stock was made in two qualities. Namely posting grade for posters or ledger sheets and in writing grade for hand written ledgers and stock cards of many kinds. A great deal of record keeping was done by hand in pen and ink at that time. A good many of the bristols were for top end recording keeping.
But I do have to mention that there were several low end poster card sheets that were specifically made for school art projects.
I really do not know how this card stock came to be named Bristol and to reiterate; each kind of bristol card stock in my part of the world had a specific name.
There were many other grades of card stock, and each had it’s own name.