A detailed investigation of the influence of substrate thickness on the static and dynamic properties of exchange-biased FeCo/MnIr multilayers fabricated onto flexible substrates by sputtering technique was performed together with the analyses based on Landau-Lifshitz-Gilbert equation. Reducing the substrate thickness to lower than 3 μm significantly enhances the exchange bias field which is attributed to the deformation of the substrates creating more pinned antiferromagnetic spins at the interface. The effect of substrate thickness on effective magnetization, effective damping coefficient, frequency linewidth, ferromagnetic resonance frequency, and static permeability is also discussed. The observed difference between static and dynamic magnetic anisotropies is attributed to the contribution of rotatable magnetic anisotropy presumably arising from the changes in the antiferromagnetic domain which also results in the enhancement of coercivity. It is evidently suggested that by using ultrathin flexible substrates one can obtain high effective permeability which is useful for microwave applications.