The Amazing Spiderman #258  Vol 1 November 1984.  Titled "The Sinister Secret of Spider-Man’s New Costume!"  Written by Tom DeFalco.

Mary Jane confronts Peter Parker shortly after returning from battling Puma.  She reveals knowing he was Spider-Man for a long time.  Mary Jane fears he is going to lie to her again.  

Spider-Man decides to visit the Fantastic Four at the Baxter Building to find out what the alien suit is made from.  Reed Richards experiments.  Used.

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