A gastight ultrathin film

All polymers suffer from a fundamental flaw: they’re helpless at stopping gas molecules from slipping through. Most polymers are made of spaghetti-like molecular strands loosely woven together, resulting in tiny spaces throughout the polymer between constituent strands. These gaps allow gas molecules to sneak through, rendering all polymers permeable to gas. In contrast, graphene offers absolute gas impermeability because of its tightly stacked, defect-free 2D crystalline structure.But polymers don’t always have to be leaky.Scientists have just unveiled a lightweight ultrathin 2D membrane that’s impermeable to gases even at the molecular level. This 2D polyaramid, 2DPA-1, matches the gas impermeability of graphene and is stronger than steel, but only one-sixth as dense (Nature 2025, DOI: 10.1038/s41586-025-09674-9).“Polyaramids are the class of polymers that include DuPont’s Kevlar, known for toughness and chemical stability,” says Michael Strano, a chemical engineer at the Massachusetts Institute of Technology, who led the study. “Polymerizing this material in two dimensions was thought to be impossible.”Strano and his team first reported 2DPA-1 in 2022 following its synthesis from polycondensation of melamine and a trifunctional acyl chloride. That procedure yielded nanofilms of 2DPA-1 between 4 and 65 nm thick (less than one one-thousandth the width of a human hair). They noticed that small microbubbles of trapped gas under the nanofilms stayed inflated for many months, and eventually 3 years. This astonishing finding led them to explore the polymer’s permeability and its potential uses.They created bulging microbubbles of the polymer by injecting several gases, including nitrogen, and then monitored the bulges for