Most of us will have experienced difficulty getting the hob exactly to the right temperature. This can mean pans boiling over too quickly, or burning sauces when we only wanted a slow simmer. A heat diffuser helps to regulate and distribute the heat from the hob to the pan.
Simply place directly onto the hob. As the diffuser warms up, it reduces the direct heat applied to the pan base and instead spreads it evenly. Very handy for those that find even the lowest setting of their hob too hot for some purposes.
Additionally, the diffuser provides a stable base for the pan, and you can also put a larger pan onto a smaller hob while keeping the heat evenly spread.