Looking to build an underquilt soon and was window shopping insulations.

ThruHiker has Climashield XP 60" wide listed as 6oz and 1.2" loft.

OWF has Climashield (no qualifier) 60" wide listed as 6oz and 1 3/8" - 2" loft.

What's the difference? Is the XP the new stuff and just as much insulation value at 1.2" as the other is at 2" or is the 2" going to work better just because it's 2" no matter what?

Can anybody tell me nuances of difference in these?