The University of Pennsylvania, in collaboration with Texas A&M University, The City College of New York, Kieran Timberlake, and Sika are working on overcoming barriers associated with carbon-storing buildings, including scarce, expensive and geographically limited building materials. The goal of the collaboration is to increase the total amount of carbon stored in buildings to create carbon sinks, which absorb more carbon from the atmosphere than released during the construction process. The project focuses on the concept of passive buildings which achieve energy efficiency primarily through separating the exterior environment and interior of a building with an airtight envelope.