The verdict is in: Two masks are better than one.

Layering surgical masks under cloth masks can decrease the amount of viral particles that reach the nose and mouth compared to using either mask alone, according to new research published in Cell Press. The surgical mask serves as the main filter, while the cloth mask improves the fit and adds a layer of filtration.

But there are some caveats, says Amy Mueller, an assistant professor at Northeastern who conducted research with associate professor Loretta Fernandez this spring to test which fabrics and styles blocked the most air particles from reaching the mask wearer’s face.