CV boot plastic or rubber

[fmugur]

Are the OEM CV boots plastic or rubber. Last time when I checked with the dealer it was plastic. Last week I got an OEM CV boot ($40) from ecstuning and it's rubber. Not sure if BMW offers two options.
Why I am asking is because on the driver side the rubber non-oem CV boot I have is 'molded' on the axel guts due to a vacuum created in there for some reason. Even though I removed the clamp a few times and put some pressure air into the boot to get it back to its normal shape it keeps squishing. I am not sure if I put the boot I just got from ecs will end up with the same problem. On the passenger side it's been ok for a few years so far.