Insulation of vapor extractor (chimney effect) with wool?

Hello, I would like a brief collection of ideas regarding the following problem:

We had an extractor hood (exhaust) installed, which vents the air through the roof. The kitchen is now installed and it is becoming increasingly apparent that a chimney effect occurs, i.e. the cold outside air falls into the living space as if through an open window.

There are apparently non-return valves, but the pipe can only be reached by removing the hood (difficult).

Now I had the idea to insert insulation material (wool). This is technically possible. Is this possible or can someone advise against it?

Other ideas?

Maybe take a look at the Berbel wall box? Insulating the pipe seems counterproductive to me... you might as well switch directly from exhaust air to recirculation air

The air outlet is on the roof, therefore no wall box is present.

Saw open the pipe in the attic and install a check valve if not already present. Under no circumstances put wool in the pipe, how else should the extractor hood still work?

You write there are apparently non-return valves, so you don’t know for sure? Maybe check it out, even if it’s not so nice to do. As a rule, the warm air should rise and not the cold air come inside. Do you have negative pressure in the apartment? Does the cold air only come in when it’s windy? What does the pipe look like at the top, is there something like a windbreak or similar?

Hello Garfunkel,

There is currently no check valve available. I meant that such things can be bought in stores. A windbreak is installed on the roof, wind is not the problem either. It is rather a constant, cold airflow downwards. Negative pressure in the living area is quite possible because of ventilation systems.

I think I have no choice but to remove the extractor hood and install a flap.