Which way up do I use the Hybrid Duvet?
That's up to how you feel. There might be times you just want a snuggle with just cotton. But to get the benefit of temperature-regulating Stratos® you should keep that side nearest to your body - it's the one indicated by the blue piping (and it's also cotton).
You can of course still use a duvet cover and we've even included 'top' and 'tail' tags to make changing the cover easy.