Because the HUMVEE was never intended to withstand such weapons, they are very vulnerable. Troops have added more armor to existing vehicles but that extra weight causes them to ride much lower than normal which may actually make them more vulnerable to explosives. In an attempt to address the issue, the Army is working with AM General to evaluate the use of lighter weight materials in the body and frame of the HUMVEE. They have used fiberglass, balsa wood, foam and carbon reinforcements to reduce the weight of the HUMVEE by 900 lbs. That weight reduction would allow the use of extra armor without riding so low, making it safer. It would also provide reduced fuel consumption which is always an advantage to military forces.
[Source: Army Times via Gizmodo]