The application testing of sodium polyacrylate prepared by spray polymerization as a textile sizer was carried out. Six monomer samples of sodium acrylate, with concentrations ranging from 30 to 45%, were prepared, polymerized, and used on textile yarns to test the sizing and thickening efficiencies of the polymer. Of the six textile yarns treated with the size, only samples 5 and 6, which had the lowest monomer concentration of 30%, had an adequate sizing efficiency comparable to that of the commercial sodium polyacrylate. A Duplan breaking figure of 3 X blank (unsized) yarn (312 in this instance) or more is satisfactory for successful weaving on an industrial high-speed loom. The two satisfactory samples had Duplan figures of 1067 and 1151, whereas the remaining four samples tested had Duplan values ranging from 393 to 769. The commercially available sodium polyacrylate size had a Duplan figure of 1146. For good sizing efficiency, therefore, a low monomer concentration of 30% or more in the preparation of sodium polyacrylate seemed desirable. Although the Duplan values for the two samples prepared with a monomer concentration of 45% (samples 1 and 2) were similar (419 and 398, respectively), the Duplan values of the samples prepared with a monomer concentration of 40% (samples 3 and 4) varied markedly (769 and 393, respectively). Samples 5 and 6, prepared with a lower monomer concentration (30%), exhibited similar Duplan values (1067 and 1151, respectively), which made them commercially acceptable as sizing agents. The thickening efficiency of the gas-phase-polymerized sodium polyacrylate was satisfactory when the polymer concentration was less than 0.2%. Above this concentration, the gas-phase-polymerized sodium polyacrylate had a low viscosity in comparison with that of the commercially available thickener.