Tyvek can wick. So can bandaids.
You want two layers, with a dead air space in between. That way, if one side gets wet and/or contams, the other side is still in tact and untouched.
Washers make great spacers for this. Check it:
Put one washer on top and one on the bottom. The dead air in between makes for a very nice security blanket.
Those lids are detailed better in post 4 of this thread:
http://forums.mycotopia.net/showpost...16&postcount=4 (BB Tek - A complete walk through; spores to LC to jars to bulk substrate)