Hi Goosey,
The mattress protector thread includes a couple of links that lead to post #1 here and post #1 here which has some of BobP’s great research into some of the membrane protectors and may be what you are looking for.
More than that and I think the law of diminishing returns, the similarities between them (based on the fabric they use with the membrane) and overly complex technical information about the different types of membranes and fabrics may lead to more time, effort, and study than it may be worth.
For those who may be more technically inclined there is a little more information and some links to sites that talk about the different types of membranes in post #2 here but this can get very technical and may not be of real interest to most people who just want something that works well and is reasonable value.
Phoenix