Why Do Post-It Notes Always Curl up at the Bottom?

3M launched its first line of sticky notes as Press ‘n Peel bookmarks in 1977, but the results were tepid. Three years later, the product was rebranded as Post-it notes and the concept soon struck gold. The company’s patent expired in 1997, but the original product’s distinctive yellow color is still trademarked. However, many Post-it users have noticed that the notes tend to curl up from the bottom when stuck on a wall, or computer monitor, probably due to the grain of the paper. Back in 2013, a clever blogger named Martin Schapendonk publicized a solution -- rotate the pad and write with the adhesive on the side. When you peel off a Post-it note when the adhesive is on the side, rather than on the top, it tends to stay much flatter.

Spencer Silver's notable work:

• Spencer Silver, a scientist at 3M, came up with the idea of a reusable, pressure-sensitive adhesive in 1968. He was attempting to invent a super-strong adhesive instead.
• For years, Silver’s idea was an answer to a problem that hadn’t been identified yet -- until a colleague began to use the prototype sticky notes to mark favorite songs in his hymnal.
• The color of the original sticky notes was not planned. The team behind Post-its began using yellow scrap paper during development, and the idea just stuck.