You’re referring to the metallic like debris that when Marcel wadded it up in his hand it returned to its original form? Also he said you couldn’t scratch it or cut it.
In order to believe that alien artifacts exist you need to believe that the government of every country in the world where they have crashed has been collaborating to keep them secret.
You also need to believe that the US government, which arguably knew about the aliens at least since 1947, conducted a nuclear cold war with the Soviet Union, and made no effort to use the supposed knowledge of aliens in its international diplomacy. I lived through the Cuban missile crisis, and I know that knowledge of an alien invasion of earth would definitely have come up during that life and death situation.
So I think the alternative explanation that someone who drank a bit too much in his retirement had an overactive imagination is a bit more plausible.
Anyway, thanks to Jesse Marcel, and his son Jesse Marcel Jr, for their lifetime careers of service to our country. May they both rest in peace.