Do you mean an inflatable like a Thermarest?
They will def. work in a double layer traveler but if it is cold enough you will get CSW (cold shoulder wrap) because the typical thermarest isn't wide enough to keep the hammock fabric from touching your shoulders.
Research a Speer Pad Extender...no longer sold but easily made that will address this.
Optimator mentioned ccf pads....they come in wide versions and several different thicknesses. I used a ccf pad this past weekend in a double bottom hammock. It was 1/8 inch thick (really thin for ccf pads) and it was good insurance that more easily packed into the backpack than the thicker ccf pads.