They look like black cycling shorts, but are made from special ballistic material crafted from silk and synthetics, which is ultra-lightweight but can stop or mitigate the effects of most small pieces of shrapnel and dirt travelling at high velocity after a blast. They have been provided with these kits to protect soldiers' most important piece of personal kit from blast injuries to the pelvic area caused by the Taliban's roadside bombs.
Many soldiers wounded by roadside bombs in Afghanistan have suffered severe injuries to the pelvic area, mainly due to the increased use of "victim-operated" roadside bombs, when the weight of a soldier or a vehicle triggers the explosion.
That means that much of the destructive force of the blast is aimed upwards, directly towards the groin and top of the legs.