There’s an old joke that goes:
A man walks into a shop and sees a vacuum bottle. “What does that do?” he asks the store assistant. “It keeps hot things hot, and cold things cold,” they reply. “Wow, that’s amazing,” says the man, and he buys one.
The next day he’s walking down the road with his new vacuum bottle when a passerby stops him. “What does that do?” they ask. “Well,” the man says, “it keeps hot things hot, and cold things cold.”
“So what have you got in it?” the passerby asks.
“Two cups of coffee and an ice cream.”
Promotional Bottles, Are They Magic?
OK, OK, I’m sorry. It’s a terrible joke. But it does have a point because, when you think about it, promotional vacuum bottles are a little bit magical. So how do they work? Well, don’t tell the kids, but it’s not magic. It’s actually all about knowing how heat transfers.
The Science of Vacuum Bottles
Heat moves in one of three ways:
- - Conduction happens when things touch, like when you pick up a cold drink, and your hand feels cold.
- - Convection occurs because hot air rises, pushing colder air out the way, like when you heat sauce in a pan – the heated molecules are rising to the surface, pushing the colder molecules down towards the heat, where they get hot and rise.
- - Radiation is hot objects releasing energy as light, which is why fire is so bright.
What Does This Mean For Your Bottles?
Vacuum bottles stop heat moving, so it can’t escape. They have a double lining, with a vacuum between layers that stops heat escaping through conduction. They are airtight, which means heat can’t escape through convection. And the reflective lining inside means radiation bounces back, keeping the heat in the liquid. Because heat can’t escape, it also can’t get into a vacuum bottle. Anything cold inside can’t absorb heat from outside. So hot things stay hot, and cold things stay cold.
Or maybe it is magic.
