Which scientific product was originally developed as a failed adhesive at 3M before becoming a massive commercial success?

The journey from laboratory discovery to commercial scientific product can be long and complex. Many groundbreaking scientific innovations undergo significant changes during product development before reaching consumers or researchers. This trivia question tests your knowledge about a famous scientific product's development journey and how it transformed from concept to reality.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Post-it Notes (originally created as an adhesive that was criticized for not sticking well enough)
Teflon (originally developed as a refrigerant that accidentally polymerized into a slippery substance)
X-ray imaging plates (originally developed as photographic plates that were mistakenly exposed)
Super Glue (originally developed as a clear plastic for gun sights during WWII)