The handle of pressure cookers is made of plastic because it should be made nonconductor of heat. The plastic used there is the first man-made plastic, which is :

The handle of a pressure cooker is made of Bakelite because it is a thermosetting plastic that acts as a nonconductor of heat and does not soften upon heating. Bakelite, chemically known as phenol-formaldehyde, was invented by Leo Baekeland in 1907. It is recognized as the world's first fully synthetic or 'true' plastic because, unlike earlier materials like celluloid which were derived from natural cellulose, Bakelite was created entirely from synthetic chemicals. While other options like Polythene (1933), Nylon (1935), and Terylene (1941) are common plastics, they were developed much later. Bakelite's heat resistance and electrical insulating properties made it ideal for industrial applications, including kitchenware handles and early electronics.