Here's an interesting photo showing the two fire damaged Darth Vader helmets. The top one from Return of the Jedi and the bottom from the trailer of The Force Awakens. Notice the fibreglass from the original prop.
Below is the part from the end of Return of the Jedi where we see Darth Vader's body (or at least his costume) being set on fire.
Here's the trailer for The Force Awakens featuring Vader's helmet.
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