Emissivity

Emissivity is a big word that talks about how good things are at giving off heat.

Think about eating a hot pizza. The pizza is hot because it is giving off heat. Now, if you put your hand close to the pizza, you will feel the heat that the pizza is giving off.

Different things give off heat differently. Some things are very good at giving off heat like the pizza. These things have a high emissivity. Other things are not so good at giving off heat. These things have a low emissivity.

Emissivity is like a rating of how good things are at giving off heat. The rating goes from 0 to 1. The higher the rating, the better the thing will be at giving off heat.

So, if you want something to give off heat very well, you should use something with a high emissivity rating. And if you don't want something to give off heat very well, you should use something with a low emissivity rating.