What is the difference between "to be made of" and "to be made from" ?
To say of "made of sth", we have in mind the original material that the object was created from, and it is a very direct and obvious relationship between the raw material and the object.
However to say "made from sth", places more emphasis on the fact that it has undergone a creative process in order to go from the raw material to the object.
"The chair is made of wood" : this tells us the simple fact that the chair is wooden.
"The chair is made from wood": this implies that the wood has undergone a transformation in order to become the chair.
This is also similar in other cases, such as die of and die from:
To speak of "die of sth", we have in mind a cause of death that is very direct or obvious while to say "die from sth", the impression is a cause of death that is not so directly observable or apparent
"Die from (cause)" would imply that you are going to die as a result of the symptoms of the cause (overworking won't kill you, but the heart attack caused by years of overworking will!)
"Die of (cause)" implies that you are going to die as a result of the cause itself (a heart attack will actually kill you!)
Hope this answers you question