This is the 6672nd most frequent Polish word.
dunna
The word "dunna" does not exist in Polish. It may be a typo or a misunderstanding.
In this sentence, 'dunna' describes a jacket ('kurtka'), indicating it is light or thin in weight.
Dunna kurtka przyda mi się na zimę.
A light jacket will be useful for winter.
Here, 'dunna' is used to describe a duvet ('kołdra'), meaning it is not heavy.
Zawsze lubiłem spać pod dunną kołdrą.
I have always liked sleeping under a light duvet.
The term 'dunna' refers to the atmosphere ('atmosfera'), suggesting it is easygoing or not oppressive.