Why are beds flat?

Last month in a Swiss hotel, I came across an idea so beautifully simple that I felt it would be immoral of me not to share it. The bed in our room, rather than having one king-sized duvet, was covered by two double-size duvets overlapping in the middle. Eureka!

Given that the Swiss are world leaders in conflict-avoidance, it seems likely the idea originated there, although I have since learned the practice is also common in Scandinavia. Back in Blighty, when one person in a double bed rolls towards the edge, they take three feet of duvet with them, leaving their partner out in the cold. This typically leads to retaliation and often escalation. The Scandi-Swiss system, by contrast, creates a buffer, a DMZ of surplus duvet, which means that bedding fights are no longer a zero-sum game.

Why has this approach not been adopted more widely? The question led me into a rabbit hole of research into bedding innovation – during which I discovered that in the 1980s as many of 20 per cent of US households owned a waterbed.