What type of reflector is used in a box-type solar cooker?

A plane mirror is used as the reflector in a box-type solar cooker.

Explanation

Plane mirrors are used in box type solar cooker because it increases the efficiency of the solar cooker by reflecting a strong beam of sunlight inside the box, which further passes through a transparent medium (glass) and infrared rays present in the sunlight gets absorbed by the black surface of the box and the box becomes hot.