Husk and powder describe physical form
Psyllium husk is the seed covering; milling reduces it to a finer powder. A mesh description helps describe particle size, but does not on its own establish purity, fibre content or performance. Compare the complete specifications.
Finer does not always mix better
Finer particles change the surface exposed to water and the texture of the prepared product. They can also behave differently during dosing and mixing. Confirm wetting, clump tendency and viscosity with a trial rather than choosing by mesh alone.
Consider the processed format
Agglomeration can combine fine particles into larger structures. Instantisation aims to improve preparation characteristics. Ask how the material was processed, what else is in it and which dispersion result is supported by testing.
For a drink powder, test the intended preparation method and drinking period. For dough or bakery, compare water demand and finished texture. A grade suited to one application may require different handling in another.