Hydration changes the texture
Psyllium husk contains water-binding polysaccharides. As the material hydrates, the mixture becomes thicker and can form a gel. The rate and final texture depend on the grade, concentration, liquid and mixing conditions.
Dispersion and hydration are different
Dispersion describes how evenly particles become distributed. Hydration describes their uptake of water. If a particle cluster hydrates at the surface before water reaches the centre, dry material can remain inside a wet lump.
For drink powders, compare initial wetting and dispersion before assessing later viscosity. Agglomerated and instantised formats should be tested against these separate requirements. They do not make psyllium a clear, non-thickening soluble fibre.
Match the test to the intended use
A bakery formula may need water binding and structure. A drink sachet may need time for mixing and drinking before it thickens. Use the recipe, water level and preparation conditions for that application.
For personal use, follow the directions on the actual product, including the required liquid. Never swallow dry psyllium powder.