Polymer science has made possible rubber tires, Teflon and Kevlar, plastic water bottles, nylon jackets among many other ubiquitous features of daily life. Elastic polymers, known as elastomers, can be stretched and released repeatedly and are used in applications such as gloves and heart valves, where they need to last a long time without tearing. But a conundrum has long stumped polymer scientists: Elastic polymers can be stiff, or they can be tough, but they can't be both.
source https://phys.org/news/2021-10-elastic-polymer-stiff-tough-long-standing.html