Why the foam on the flaps in the heater box?

[Rs2-GTi]

I had out my heaterbox some years ago, and when installing it, I noticed that the round holes in the flaps had lost its foam. After this, the heater never really got warm. The car has been parked for a couple of years, and now I'm getting it back on the road, and in Norway - we need all the heat we can get! ?

I'm gonna take out the box and seal the flaps, I've bought bitumen cardboard with glue for sealing and sound profening. But it puzzles me - why did Audi use foam in the first place, and why the holes? Is it suppose to blow out if something something happens? It it just for saving weight? Is it for letting some of the could air get in at all times?

Basicly I'm woundering if I need to use foam and spray glue to fix it, or if I could use bitumen. I found a video on Youtube of this guy fixing his heater box, and he used something that looked like the bitumen that I got. So really just want to know why to foam, and why the holes.

[John.]

I think foam because it's cheap and easy to work with? The holes are probably so some air gets through so as not to cause either too much vacuum or pressure(?) so as when the motor is at full speed you can move the flaps easily without fighting the vacuum/pressure(whatever!).

Just my thoughts.

[Tractor Dave]

Neoprene sheet works very well. I think the holes are there to make the flaps light so that the electric version can move easily. My Ur even had holes.

[newsh]

As Dave says, this stuff works well

[Rs2-GTi]

Good theories for the foam. I'll just try to go for the bitumen sheets for now, as I can't seem to get the neoprene or foam with glue locally. And right now it's -6 outside, and I need to take the car for the review for the MOT without an inch of ice on the windows. Thanks for the input!

[Tractor Dave]

What is the melt point of the bitumen? You might regret that.
Why not use plain neoprene sheet and high temp spray adhesive?

[newsh]

Or just use duct tape. (Gaffer Tape)
I definitely wouldn't use the bitumen, it's too heavy and I think it'll be affected by the heat, probably stink too lol.

[Rs2-GTi]

Alright - I'll se if I can find neoprene. The problem is finding it up here above the arctic circle, and if I order in, it will most likely take a couple of weeks before I get it. And I need to use the Coupe to haul some trailers with firewood ASAP.

[mdz]

Check your nearest hardware store. I've used drywall soundproofing tape countless times and it still holds 10 years later.

[Rs2-GTi]

[Rs2-GTi]

I found this foam at the local furniture upholstery guy. He was a bit sceptical if it would handle the heat, but I tried it with a heatgun, and it started to melt about the same time as the old material - but differently (made horrible gasses). I can't get neoprene anywhere local here, so except ducttape this seem to be my only option. But I don't want to do this twice, so any input is appreciated.

It could take more heat than my skin could without reacting. Should I order online and be without the car until about Xmas or use this?