Which tissue endotherms maintain body temperature?

The Adipose tissue helps endotherms maintain body temperature in cold weather.

WHAT IS THE ADIPOSE TISSUE?
Adipose tissue, commonly known as fat, can be found all over your body under your skin. It also can be found packed around muscles, within bone marrow, and in breast tissue.

WHY IS IT IN MY BODY?
Its main role is to store long-term energy. Think about it this way, if you're overweight, your body has captured a lot of energy that it doesn't really need.