Impact explosives explode upon contact with the landscape or the players Sack person and will clear out anything in its blast radius, except things that won't explode (metal, stone, etc.). However, if the players Sack person picks it up carefully, it will not detonate unless coming in contact with another material very quickly. They can be useful for dropping on Sackpeople or for carrying with a jetpack to clear obstacles. Despite it's usual uses it can be triggered with a switch.
Trigger explosives are explosives that explode when activated by a switch. They can be useful for blowing up objects from safe distance, but also as traps.