Data was collated from literature sources for material properties not measured in this study (Supplementary Table ). Material indices (MIs) used to evaluate the performance and the environmental impact of the materials were derived for the design of stiffness-limited and strengthlimited films or sheets, for which the free variables were the thickness of the film or sheet and the choice of material. MIs included those for material efficiency, material cost efficiency, minimal greenhouse gas (GHG) emissions, minimal energy usage, minimal water usage, and minimal environmental lifetime (Supplementary Table ). To evaluate tradeoffs between MIs, a value function (𝑉) was used to convert performance to monetary value using exchange constants (Equation ) , 𝑉 = 𝑚 0 (𝐶 $ + 𝑎 𝐺𝐻𝐺 𝐶 𝐺𝐻𝐺 + 𝑎 𝑤𝑎𝑡𝑒𝑟 𝐶 𝑤𝑎𝑡𝑒𝑟 + 𝑎 𝑝𝑜𝑙𝑙𝑢𝑡𝑖𝑜𝑛 ℎ 0 4𝑘 𝑑 ) (5) where 𝑚 0 was the initial mass of the item, 𝐶 $ was the specific price of the material, 𝑎 𝐺𝐻𝐺 was the social cost of CO2 , 𝐶 𝐺𝐻𝐺 was the specific embodied GHG emissions of the material, 𝑎 𝑤𝑎𝑡𝑒𝑟 was the social cost of water usage, 𝐶 𝑤𝑎𝑡𝑒𝑟 was the specific embodied water usage of the material, 𝑎 𝑝𝑜𝑙𝑙𝑢𝑡𝑖𝑜𝑛 was the product of the frequency for an item to leak into the environment and the social cost of plastic pollution, ℎ 0 was the initial characteristic length (i.e., the thickness of the film or sheet), and 𝑘 𝑑 was the specific surface degradation rate. The relative value was used to calculate the value of hypothetical items that satisfied the same engineering requirements as a reference item of known dimensions and mass. The relative value for the nth component of the value function between the ith material and reference material can be expressed by Equation 6 .