White insulation behind door panel?

A few days ago, I installed the BAVSound speaker upgrade for my base audio. This involved taking off each interior door panel- a fairly easy process. There is white insulation that lays over the foam door "membrane." My passenger door has it, but the driver door doesn't- the staples and tiny bits of leftover material are there, so it was there at some point, but gone now.

I can't seem to turn this up in a parts search. Does anyone have any idea?

BTW, I don't think I like the speaker upgrade... frequencies in the voice range are now VERY forward, to the point of being overbearing. Siri's voice is in that sweet/resonant spot, seems like her specific frequency is a good 10-12db higher than with the factory speakers. I can't dial it out with the Tone, even the EQ settings on my iPhone can only do so much. I've asked for some guidance from BAVSound, but I may be sending them back.

I know what you are talking about but don't know the part number either. Given that your vehicle seems to have had it on the driver's side, it indicates at some point someone took off the panel and ripped that part off. If I were you, perhaps you can replicate it yourself with better sound deadening material for both sides. As it is, it's a pretty useless piece of material and I'm shocked it's so cheap on the insides of the panels in this car. It's no wonder it rattles so much over rough roads and sounds very plasticky in general. They could have done a much better job insulating the vehicle NVH wise.

I haven't taken off my door panels so I don't have first-hand experience with the material, but two thoughts...

If it's thin and light it's likely a moisture barrier like Tyvek:
https://en.wikipedia.org/wiki/Tyvek

If it's thicker and sticky on its back side it's likely a sound isolation product. Those are usually composed of mass-loaded vinyl (MLV) and a well-known aftermarket version is Dynamat:
https://www.dynamat.com/applications-industries/automotive-and-transportation/

I would guess the missing material was a moisture barrier.

MLV is heavy for its relative thickness and having read early i3 articles, I've seen quotes from designers stating that they "sweated every gram" – that makes me think BMW wouldn't have added a lot of heavy soundproofing.

Just adding on here to say, "thanks" Egbert, for the Bavsound feedback.

They used to advertise heavily in BMW-targeted sites and publications and I've wondered how one of their upgrades would sound.

I like a balanced presentation and from reading your post it seems like the Bav drivers might be too forward for my tastes.

I believe, the white acoustic insulation material is "Thinsulate" by 3M.

I'm exploring the Bav drivers and from reading your story, it looks like it could be too upfront for my standards.
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