It will shrink a lot! I think they say it shrinks up to 20%?? I could be wrong but I know it's a lot so definitely prewash/dry twice before sewing or else you'll size it wrong.
For the same weight-hemp is more absorbant than cotton and it's also more resistant to bacteria because of the natural fibers.
There are lots of types of hemp like cotton-hemp jersey and hemp fleece are the most common for clothing and diapers as far as I know.
When you get it be prepared that it comes in a tube that you cut in half to get your full size.
If you're using it for dipes I think it's great but I do have to watch for detergent build up-I double or even triple hot wash about every 3 weeks without soap to get the residue out.
Good luck
Ann