realistic insulation values for foils / bubble foil nowadays or still questionable?

[Mr Gus]

Bearing in mind the oft mad claims for quilted / bubble foil product some years ago, ...anywhere trustworthy to make decisions easier these days?

I'm looking for a small amount for above the cold water tank in the same section as my hot water tank, just BELOW the loft & to wrap the bit that still irks me (by the HW tanks closest wall edge) where I have about 20 mm tight free space.

[Stinsy]

PIR is so cheap these days and the best thing per mm you can get. Comes in 12 or 25mm if you can make that fit. Otherwise bubble wrap/cardboard is definitely better than nothing but don’t pay for it recycle packaging…

[Mr Gus]

It is packed to what many would consider ridiculous, however this segment is both tight & tightknit pipework, I've dome what I can, everything else is "Lego formatted" for easy reassembly, some would be slid some taped, some staples to the ceiling, it's needed in this format, no choice.

Card would do something but it's a potential fire hazard (Like those towels & toilet paper) & it's vapour near card which may sag.