Flask venting, breathable plastics?

[Djarum Black]

I was doing some research on replate flask venting because I'm having trouble finding a good way to do it.

I've seen people use little round bandaids to vent a flask jar with a hole drilled in the top. I have also seen people who use tightly woven cotten and some other type of material.
However I swear I heard somewhere that there is a plastic that will allow air exchange on it's own without contamination of the flask. Is this true? Is there such a plastic container of some kind thats being used for this purpose?
For those of you out there who flask, what method do you use to vent your replate jars/flasks?

A big thank you in advance to anyone who can help me with any information.

[Shadow]

I saw new flasks with special ventilating discs. You can read more here vented plant culture containers

[phragguy]

I use flask from Phyto-Tech that are plastic round containers that the lids are vented around the edges,work well. But can only be used once.
Some of my replate jars have no air exchange at all.
Not a prblem for me.

[Ray]

All plastics are permeable to some extent, but I'm not aware of any that are sufficiently so for venting flasks.

[Matthews]

I agree that Phyto-Tech has great flasks. They used to sell orchid flasks, but now the only thing they do with orchids is a flasking service.