Inflatable mats are made with an adhesive backed fabric, baffles are adhesive coated both sides. The adhesive is heat sensitive (ie.. to a hot iron).
Here are some pics from modifying a regular synmat (that became a synmat short lol) but with some lateral thinking there may be some other applications.. you can also buy the material itself (for a repair)
This one had a minor tear

Trimmed to length (I'd use a knife or scissors for the initial cut then trim later with the hot knife (if you have one)):
I use a straight edge for the cut and to run the iron along (and a coffee tin as a template to round the cut to the side of the mat ; ) )
For an insulated mat you'll want to remove any insulation from the area to be resealed:
Shazam... mini mat: