Air vent insulation

I was recently painting our sitting room and removed the vent cover, i noticed that there was just a wavin pipe sitting very loosely in a roughly made hole in the wall, should this be sealed on the outside wall to help with insulation? I checked all the other vents and they are all the same.

Any info would be appreciated.

Air Vents are very inportant and should not be blocked!!

Depending on heating system type, there may be a danger of Carbon Monoxide Poisoning if vents are blocked.

i'm not talking about blocking the vent, i am just wondering if the outside of the wavin pipe should be sealed to stop cold air going into the cavity of the wall??

Expanding foam?