Delamination.
Had it happen to my first Exped after about three years while on a caribou hunt. Annoying, but not life threatening.
Took it in to the mountaineering store i bought it from and they just handed me a new one with no questions asked and sent me on my way. The replacement has been going strong for five years.
Ive had the same pad for 5+ years with no issues and two of their other pads no issues. Love them. Glad to know they stand behind their product if this does happen.
I had a baffle blow out in the middle of the night last year on a UL7 Synmat. Exped replaced it no questions asked. They also said they had changed the lamination in the lighter pads and thus far had no baffles blow out after changing it.