There are numerous technological drivers for the use of thin (sub-1 µm) and ultrathin (sub-100 nm)polymer films and features. The stability and reliability of these confined polymer systems are critical to numerous existing and emerging technologies such as next-generation lithography, lubricating coatings, sensors, and organic electronics. It is widely accepted that the physical properties of thin polymer films can deviate substantially from their bulk counterparts. However, most experimental studies have focused on elucidating the thickness dependence of the thermal properties in thin polymer films. Direct measure of the mechanical robustness(e.g., response to deformation) of confined polymers films would be extremely helpful to determine if the mechanical properties display similar deviations from bulk response. In this talk, the elastic moduli of ultrathin poly(styrene) and poly (methylmethacrylate) films of thickness ranging from 200 nm to 5 nm are determined using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.