10% Polysorbate 20 is a ready-to-use solution of polysorbate 20 (Tween-20), a nonionic surfactant, in purified water. The 10% stock allows accurate dosing to low working concentrations. The 1 L fill supports laboratory and pilot-scale use.

It is commonly used as the surfactant in immunoassay and western blot wash buffers, and to protect proteins from aggregation at air–liquid and container interfaces in formulation development. Add 0.5 mL per liter for 0.005% or 5 mL per liter for 0.05%.