Made of or made from

Actually, the rule how to use 'made of' and 'made from' is very simple.

How to use made from

We use 'made from' when we want to show and when we know that the material was created by changing another one.

Headphones are made from plastic. (plastic was manufactured from other different materials)

The vase is made from glass. (glass was manufactured from sand)

How to use made of

We use 'made of' when we know that an object was created without modifying another one, when we speak about the basic material. Also, we use 'made of' when our object and the basic material resemble each other. 

The chair is made of wood.

He gave her a wonderful ring made of gold.

The dress is made of cotton.