If this mat gets wet, is the down insulation...
If this mat gets wet, is the down insulation affected?
If the outside of the mat gets wet, the down insulation will not be affected since the pad is airtight (and thus watertight). If the inside of the mat gets wet (if you somehow allow water in, or breathe directly into the mat (the moisture in your lungs/breath)) then the insulation will decrease. But the included pump should prevent you from breathing into the mat directly and prevent moisture from entering the inside of the pad.