Go to profile >> material.
Click the name of the material.
In the category box, click the drop down icon.
Click +New Category and enter the category name.
Click add button.
Your defined category will be listed.
Go to profile >> material.
Click the name of the material.
In the category box, click the drop down icon.
Click +New Category and enter the category name.
Click add button.
Your defined category will be listed.
Read more about it here