In my look into the world of shaving I've seen claims that it is better to shave after a shower because the hairs will absorb water and soften, making the shave easier. Likewise, I've seen it claimed that natural hair brushes (i.e. boar and badger hair brushes) should be soaked before use. My question is: do the hair fibers actually absorb water, presumably thickening in the process, or does the water just adsorb onto the surface (maybe lifting the scales in the cuticle) meaning you can wet hair in aggregate, but it doesn't soften when soaked? Especially, is there a side-by-side comparison of a single hair under a microscope before and after soaking showing what happens?
Researching this answer took me to some strange literature, but it appears to suggest a little bit of both (at least for human hair, which is porous, implying that some water can suffuse through the cuticle into the cortex). For example this paper looks at the impact of this effect on drug testing.
There's also a few papers in cosmetics science journals describing various elements and effects of increased hair porosity, but I was unable to find one primary citation which characterised the trait.