Yep, probably same material I have in my current Jeep (brand ??). My concern with HDPE is the deflection temperature is rated at just 150deg F. That's not a whole lot higher than the interior temps the Jeep may seen on a blazing summer day. I think we're OK at the -180F lower end
My complaint with my current slush mats is they have deformed. The edges have curled, causing some interference with the gas pedal. - from what appears to be high temps. When I lay them on the driveway to dry after washing, they seem to soften and return to more normal shape, but its only temporary.
I cannot say for sure my current mats are HDPE, but guessing its a similar formulation.