Anhydrous sodium sulfate (Na₂SO₄) contains no water of crystallization and is the preferred form for detergent and glass applications due to its higher active content and easier handling. Glauber's salt is the decahydrate (Na₂SO₄·10H₂O), which is bulkier and less stable at higher temperatures. Both fall within the sodium sulfates heading, but the grade and form should be specified on the invoice to support correct classification and to meet buyer specifications.

Yes — a significant share of global sodium sulfate supply is recovered as a byproduct from rayon (viscose) fiber production, kraft pulp mills, and certain chemical manufacturing processes. Byproduct material is often priced below natural-source or purpose-made product, which can create competitive pressure on domestic producers and may be a factor in antidumping investigations. Importers should monitor trade-remedy developments when sourcing from major producing countries.