The effect of sizing on bending rigidity in fibre bundles was investigated. Particular attention was paid to the effect of film formers and anti-static agents on the behaviour of glass fibre bundles under forced packing conditions. The bending rigidity of different types of bundle was estimated through the nail test, the Kawabata test, and packing stress experiments coupled with micromechanical analysis. An analytical expression describing the packing stress versus fibre volume fraction was derived for bundles with elliptical cross-section. The predicted values for bending stiffness of bundles were in good agreement with direct experimental measurements. These showed that sizing formulation may affect bundle rigidity and the compressive behaviour of dry fibre suspensions.