InsulTubes are simply long, non-tapered, pleats that make a 3/8" tube and serve the purpose of keeping the layers of IX from touching.
plastic sheet sandwiched between 2 sheets of highly breathable fabric.
What has puzzled me is why the 2 fabric sheets?
I suspect that the explanation of how/why IX works will include the term "Boundary Layer"
I also suspect that Mac's InsulTubes/Baffles help keep the proper gap between the IX layers so the boundary layers are maintained. Brilliant!
My last physics class was 35 years ago, and much has been forgotten, so any corrections or enlightenment would be welcome.