In one Parisian apartment building, the residents rarely turn on the heat, even in the dead of winter. That’s because the walls are filled with “hempcrete,” an innovative insulation that is better for people and better for the planet. 

The revolutionary material doesn’t contain harmful synthetic ingredients like fiberglass or foam board, but rather, it’s made from a blend of the woody core of the cannabis plant, called hemp hurd, plus water and lime. The resulting insulation acts like a toxin-free sponge that absorbs moisture from the surrounding air when it’s humid and releases it again when it’s dry. This regulates not only temperature but also air feel as well for improved comfort. 

Hempcrete is a healthier insulation for humans as it reduces exposure to toxins in living spaces, but it also has tremendous environmental benefits. Unlike commercial insulation production, which generates emissions, in eight weeks of growing, an acre of hemp can sequester an impressive 10 tons of CO2. That’s more than an acre of trees can sequester in an entire year. Plus, when combined with lime, the resulting hempcrete continues to absorb carbon and sucks up emissions from other construction materials. 

One analysis from the Healthy Materials Lab found that hempcrete generates roughly three times fewer carbon emissions than walls built with conventional methods. Although hempcrete is about 20 percent more expensive than traditional insulation, it pays off in lowered energy bills and environmental benefits. 

Paris first began incorporating hempcrete into construction in 2012. Its social housing department, Paris Habitat, saw an opportunity to expand sustainable design within government-funded subsidized housing projects. In this way, some of the city’s most vulnerable residents experience the health benefits of natural insulation and also reap the financial rewards of lowered air conditioning costs. So far, Paris has installed hempcrete in 40 subsidized units with more planned for the near future.