Pulpboard is generally regarded as of poor quality ~ but I treat the wording with caution. Pulpboard is frequently misunderstood ~ and maybe by me. I am happy to stand corrected by those who know ~ someone with a history in the pulp conversion industry.
The implication is that the pulp is poured into a mould, or otherwise formed into material of suitable thickness, without any particular additives or working. Handmade papers are of high quality ~ but the pulp is carefully shaken and mixed in the deckle so that the fibres entangle sufficiently to give it strength. Pulboard has to be thick because the fibres are not enmeshed and the only strength is obtained by the thickness of the board. The best example I can think of is blotting paper ~ but who remembers that?
The quality of the pulpboard I have so far described can be improved with a little working. Perhaps some adhesive in the fibrous mix ~and a little rolling to even out the bumps and squash the fibres together. The picture framing trade makes extensive use of such pulpboard. It is carefully rolled to aspecified thickness and then covered on each side with suitably tinted paper of good quality. Such boards are made to various specifications ~ the best being acid free and of conservation quality. Several manufacturers each make dozens of different colours. They even produce numerous tints of white ~ off white ~ arctic white ~ snow white ~ eggshell ~ and so on. They are all of excellent quality. Because of the cloud of doubt over the word pulpboard it is rarely used to describe them ~ artists' mountboard would be a safe description. The central core appeals to the frame maker because it is easy to cut and evenly and finely fibred.
I suspect that American descriptors of various board types vary from ours.