I have a thermarest ridgeRest pad that i used to use with my GoLite Breeze.
Simply cut it down to the desired length to reduce the weight by cutting the desired number of inches off of the foot end of the pad by cutting straight across the pad.
The "cut-down" is not a vertical/thickness cut-down. It is a length cut-down.
Furthermore, you could also reduce the wt. a little bit further, by cutting a "mummy" type of shape off of the remaining rectangular pad. That is, cut the four rectangular corners off the remaining pad, which was just previously cut-down to a shorter length, by making angular cuts. I know this description is NOT very clear, so go to the POE website & look at their pads - they come mfr'd with that "mummy" cut shape.
You can weight the end result (the best way to determine the wt) or if you leave it in a rectangular, non-mummy shape, it's a simple linear calculation to calculate the wt. of the cut down pad.
e.g., using a standard ridgerest's published figure
14oz*new-length-in-inches/72inches =new wt.
conversely, you could work the equation backwards, picking a new "target" wt & then solve the equation algebraicly for the "new length".