What damage type is a Kobold's explosion?

I've built an Apprentice character that only has about 500 HP and Kobolds in the later waves of challenges have started to one shot my character. This makes it fairly difficult to repair towers once I get behind.

So, I'm curious if Kobold explosions are a specific damage type, like fire, so I could build up some resistances against them so they don't destroy my poor towers only Apprentice build.

The damage type is fire. I would, however, focus more on building so that they won't ever hit you or your crystal, seeing as they get pretty powerful.

Source for damage type: http://dungeondefenders.wikia.com/wiki/Kobold