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A weekly show where we endeavor to answer one of your big questions. This week, a bunch of people asked, "Why doesn't glue stick to the inside of the bottle?"
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Hi, I'm Craig. I'm really good on Twitter, and this is Mental Floss on YouTube. Today, I'm gonna answer a big question that we get asked a lot around here: why doesn't the glue stick to the inside of the bottle? So thanks for that question Joe May, Spencer Solomon, Rachel Harris, epicXpie, Sarah Hemphill, Joe W., probably my mom, and so many more of you. Let's get started.


So, there are a few different types of glue. I assume most of you are referring to regular white craft glue, so let's stick with that for now, but I'm also going to tell you a little about super glue. Get excited. Super excited.

First, let's talk a little about the composition of white craft glue. Nowadays, productions like Elmer's Glue are usually synthetic, rather than made from animal parts like they used to be. They're water base and contain some synthetic polymers, which are substances that contain repeating molecular sub-units. Polymers make up things like plastics, rubber, and glue.

We don't know exactly which polymers are used, because brands like Elmer's tend to keep their formulas secret. Good business. That's good business. Take note Mental Floss.

One polymer that's probably used in many white crafts glues is polyvinyl acetate, also known as PVA, or "puhvuh". Craft glue is typically water based, which works well with "puhvuh" because it's water soluble. Then it becomes the perfect material to use as an adhesive for porous things like paper and cloth. Or Swiss cheese.

So why doesn't it stick to the bottle? Get to the question, Craig. Well, it has to do with those ingredients. According to the Elmer's website, "As long as the glue remains inside the bottle away from air it remains a fluid. Glue hardens when there is a loss of water from the formula. Exposure to the atmosphere will cause the water to evaporate and make the glue harden."

Super glue, on the other hand, is made from cyanoacrylates, which also are adhesive, but they're more fast-acting, and strong, and super. In order to become sticky, the glue needs a small amount of water, which it can get from the surface of most items that people try to glue together.

So, in a bottle of super glue, there should actually be no water, or else it will be at risk of drying out. If it comes into contact with water, it will stick to the bottle.

Incidentally, I'm the same way. Someone pour water on me. I will stick to anything. Come on. You don't want to see that? Why are you looking at me in disgust?

Thanks for watching Mental Floss on YouTube, which is made with the help of these sticky, sticky folks. If you have a big question of your own you'd like answered, please leave it below in the comments. I'll see you next week. I hope you... I'm not going to make a "stick around" joke. I'm not gonna make a "stick around" pun.