Speaking of Tom Bihn bags, look at the pains they go through testing back panel fabrics:

In an effort to better understand what we were experiencing, Tom’s longtime friend Robert Swarner (sculptor, helicopter pilot, product designer, big wall climber and machinist) came up with a device that’d allow us to scientifically evaluate the effectiveness of Dri-Lex® Aero-Spacer® mesh. Tom and Robert modified a Synapse and equipped it with Robert’s mobile heat sensors and data recording device, which we named The Swarner 5000 Datalogger. The Synapse had a back panel split down the center vertically: one half was spacer mesh and the other half was 1050 Ballistic (both sides were padded with closed-cell foam). Over the course of the last year, we’ve used this special Synapse on day hikes long and short, on hot summer days and cooler winter ones, and usually on hikes with big elevation gains.