Magic Balloons used to be a kit with a tube of coloured goo (like squishy plastic) which you moulded around the end of a drinking straw, and then blew really, really hard (so your cheeks hurt). Then it made a bubble made out of really thin stretchy plastic and you sealed the end and took it off.
I think they were called Magic Balloons because you could touch them without them popping which I remember thinking was pretty magic. I had red and blue ones, and the plastic stuff stunk!
Do You Remember Magic Balloon?
Do You Remember Magic Balloon?