This thread is for general discussion of the design and construction of insulation made from foam sheet (whether it be Insultex or one of the various polyethylene/polypropylene materials made for shipping/packaging/&c.).
Foam sheet appears to work well for insulation, especially when two or more layers are used and those layers are separated to minimise heat conduction. MacEntyre has been using pleats (InsulTubes) but I think there is opportunity for improvement.
Using a separate layer of expanded mesh made from foam sheet seems promising. It's labour-intensive (though easily tooled once the dimensions are optimised) but I think it would work well.
Alternatively, the layers could be separated with a replaceable air bladder (plastic bag), a little down, found materials (dry leaves/grass), by direct inflation (assuming airtight material and construction), &c.