It is a plastic inner drive housing inserted into a metal outer case housing.
I transferred over 500 gigabytes of images in one setting and it was a little warm but not at all hot.
The drive is the type that slides forward ( push-up) from the outer housing. The first time it was very tight and I thought it may be defective but I just forced it in and out several times until it worked smoothly. I suspect the plastic housing on the drive was designed purposely to be a tight fit into the metal outer case housing. Overall the drive works great and I am very satisfied. Hope this helps.