Changing to lighter bedding
Short answer: Change when the nights stay above fifteen degrees. That is typically May in Denmark, but go by the thermometer rather than the calendar.
What you change
The duvet first. Go from a winter duvet of eight hundred grams or more to a summer duvet around three hundred. That is the change that alters the most.
Then the cover and sheet
A thin bamboo cover lets the heat escape rather than holding it in. Combined with the light duvet the difference is noticeable on the first night. See bamboo bedding.
What you put away
Wash the winter duvet and covers before packing them away, and store them with air around them. See bamboo sheets and bamboo fitted sheets.
Frequently asked questions
When is it too early
If you wake up cold two nights running, it was too early.
Can you use two thin duvets
Yes, that lets you adjust gradually.
Should the mattress be aired too
Yes, take the sheet off and let the mattress stand for a day.