Plastic tubing? Im not sure what you mean.
I did the mod on them, removing the paper screen and even tried some cotton in place of foam. The stock version is just too bass heavy for my needs, im sure most people will just love it. But, for me its just too thick and when I use my Cmoy BB 2.02 its WAY TOO MUCH BASS. But with the screen removed its much nicer, equally as punchy and the bass is less thick.
So, as for the plastic thing you mentioned, Im again not sure what you mean. I don't see any plastic around the tips that are made of pure memory foam. The only tube I know of on them is right under the tips, but its rubber and grey.