Watercolour is one area in which the weight of the paper plays a pretty dramatic role in the outcome. Typical paper choices range from 90 lbs, 140 lbs, and 300 lbs, with corresponding increases in price as the weight goes up. There are also options like 200 lbs and 400 lbs out there as well.
Typical usage, for professional watercolour, seems to generally be 140 lbs (light water usage) and 300 lbs (heavy washes and wet layers). Carrie, of "Watercolor Misfit" fame, posted a video today on this very topic:
That also got me thinking about paper weight in general, notably how it gets weighed, and what that actually means. Turns out, it's not really all that cut and dried. In North America, particularly in the US, paper weight is in pounds per ream of 500 sheets, for much of the rest of the world, it is grams per square meter (gsm).
Okay, so what? Well, the measurement in pounds per ream is not actually an equal comparison between types of paper since it's based on the base size of the paper type. For example. watercolour paper base size is 22" x 30" and sketch is 25" x 36" and so if we had the same "weight" of paper for each, that would not actually result in paper of similar thickness and heft since the total amount of actual paper material of the sketch paper would actually be more by volume for a ream of the same number of sheets.
However, gsm is a direct comparison between paper types since the weight is based on a single sheet of paper that is 1 meter by 1 meter in size and thus ignores the concept of reams and base-paper size. It's a measurement of sheets of paper of the same length and width and so 300 gsm watercolour paper and 300 gsm drawing paper would be quite similar in heft. Mind you, they are different material, cotton vs wood pulp, but that's not going to make a huge difference thickness.
Confused? Well, Strathmore has a good write-up on the topic, worth a read, or you can just ignore relative comparisons and know that the heavier the paper, for watercolour, the less buckling and warping you will get.