Yep. The insulation is rectangular bits of foam stuck to the upper inside of the mat. Quite a few have moved. It's a shame because as far as I can tell that aren't really any good budget options for inflatable sleeping mats.
One of these with a cheap foam pad on top. https://www.ebay.co.uk/itm/Emergenc...at-Outdoor-Mattress-Sleeping-Pad/133485009172
Are the Naturehike and Flextail deemed crap? To be honest, rather than spend £60 here and there on potential options, it might be best to just use a foam mat until you can save for a £100 TAR/Exped/Nemo/etc.
So what he is saying (but not quite saying) is that its a good idea to place a silvered reflective mylar or foam sheet or underneath most kinds of sleep mats (and probably more effective than having one inside a mat) ... maybe cheaper too ?
I think similar subject has been discussed here favouring putting the foam sheet on top of the air mat, which makes sense but not always the easiest to use.