The foam generator and applicator of experimental scale for foam siring were specially designed and prepared, and results from studies of foam sizing were presented. Foam siring conditions using this device and foaming efficency of several size materials were described. The size add-on, selected physical properties and conditions of the yarn surface were demonstrated. Properties of polyester/cotton yarns and nylon filament yarns sized using foam were equivalent or superior to those of similar yarns sized conventionally.