From health monitors and smartwatches to foldable phones and portable solar panels, demand for flexible electronics is growing rapidly. But the durability of those devices—their ability to stand up to thousands of folds, flexes and rolls—is a significant concern.

New research by engineers from Brown University has revealed surprising details about how cracks form in multilayer flexible electronic devices. The team shows that small cracks in a device’s fragile electrode layer can drive deeper, more destructive cracks into the tougher polymer substrate layer on which the electrodes sit. The work overturns a long-held assumption that polymer substrates usually resist cracking.

“The substrate in flexible electronic devices is a bit like the foundation in your house,” said Nitin Padture, a professor of engineering at Brown and corresponding author of the study published in npj Flexible Electronics. “If it’s cracked, it compromises the mechanical integrity of the entire device. This is the first clear evidence of cracking in a device substrate caused by a brittle film on top of it.”