Thermistors for 3D printers are devices used to measure the temperature of heating elements such as nozzles or the build surface. They play a crucial role in maintaining a stable temperature during the printing process by providing feedback to the printer controller for heating regulation. Thermistors are typically placed in proximity to the heating element and send temperature signals to the controller, which then adjusts the power to the heater. They are essential for achieving the correct temperature conditions for different types of printing materials and for ensuring high-quality and reliable printing results.