It's really pretty minimal. Adding 5" width to the full length 72" pad yields about 360 s.i. of extra fabric (not accounting for baffle welding). There are 1296 s.i. in a sq/yd of fabric and let's call that 1oz/syd for convenience. So around a quarter ounce, or a half ounce to be generous & conservative? If you take that 25" pad and whack off 12 inches you lose 240 s.i. and for all intents and purposes achieve the same weight as the 20x72 (about 60 s.i difference, negligible), but now have a 25x60 that accommodates elbows and side sleepers better, most of the time. And 60" is considered pretty long by UL-mindset standards. With wispy UL fabrics such as used here and only a tiny bit of adhesive weight to consider, or a little insulation weight as applicable, we're just talking very small weight differences...not like the much more appreciable differences, say, in a foam self-inflating pad.