What was inside Stretch Armstrong?

The file

A blond, muscle-bound figure in black trunks that you could stretch to four feet and watch slowly shrink back. The question every kid asked was what was inside, and the answer, corn syrup, was learned by cutting one open.

Every Stretch eventually split and leaked sticky goo on the carpet, which is the shared ending of the story. Original ones that survived intact sell for serious money now, precisely because almost none did.

Sources: Wikipedia — Stretch Armstrong