If your grandmother is anything like mine, the moment the frost hits the ground she’ll be calling you up just to check you’re wearing a vest! I’m sure she just wants me to be warm, but at the ripe old age of *cough splutter* I find myself capable of dressing myself!
But maybe there is something in this vest stuff? Why are they good to wear? Well, it’s because more layers of clothing mean more trapped air layers between you and the outside. Which doesn’t sound all that wonderful until you think how bad air is at conducting heat. Sure, it’ll move heat around by convection, but there’s not really much space under your jumper for a breeze to start up!
As we learned before here heat travels by three main methods, convection, conduction and radiation. A layer of air between the hot surfaces and the cold means that these three effects are minimised. Air is an insulator because it doesn’t conduct heat very well. Sure, there are better insulators out there, like roof lagging, but that certainly doesn’t make for an attractive or comfortable outfit!
And just as we can heat ourselves up with a vest to trap air, we do the same to our houses. Double glazing is the architectural equivalent of a vest, with the two panes trapping all that insulating air inside to protect you from the cold.
If you don’t have double glazing, you can also make it yourself, although take this as a warning that people like to poke holes in it for fun. Simply take cling film, stick to the edges of the windows and fill in the centre leaving your insulating layer of air trapped. Apply gentle heat with a hairdryer to shrink to fit and there you go, your windows are now wearing a vest. My grandmother will be pleased!