Why are blankets square?

Answer 1

I assume you mean, why are blankets rectangular? Most of them aren't exactly square.

1) Because beds are rectangular and the blankets have to fit them.

2) Because people are roughly rectangular and the blankets have to cover one of them, or two lying side by side. If two people generally slept crossed over each other at right angles, it might make sense to have X-shaped blankets. But they don't do that, mostly.

3) Because it's easy to cut a rectangle from a roll of material, without wasted fabric. If blankets were round, for instance, then when you cut them from a bolt of cloth you'd have these odd concave bits left over. What are you supposed to do with those? You can't stick 'em back together; they're just wasted.

That last point leads to the question, why does fabric come in rolls. Why can't we just weave something the exact size and shape we need? Probably someday we'll do just that, and if you look at knitted things, those can come in any shape, and often do, especially if they are knitted by my aunt Mattie, and there's no waste material.

But at the moment it's much less expensive to weave most things on a loom, which produces a long strip of fabric of a constant width, with the threads crossing at right angles.