The subbase is the aggregate material below the “base” which is your first layer of pavement. It is composed of soil, gravel, reclaim, stone, etc (depending on your area and current situation). It is important that this subbase is properly constructed of the right material and compacted and graded properly as it is the load bearing layer of your paving project (i.e. your paving project will only be as successful as your subbase). Do you see dips, potholes and damage to your existing pavement? Many times this is an indication of subbase integrity.