Some knee and elbow pads that are commonly available for ACUs are cheap and not inexpensive.
For example, the knee pads pictured below are a thin foam rubber. Because they are thin, they do not provide adequate padding or insulation from a cold ground.
In addition, when immersed and compressed in water, they absorb water and retain it. This makes for continually cold, wet knees. Not good.
This Instructable demonstrates how to make inexpensive knee pads that provide more cushioning and insulation than these cheap knee pads. Most importantly, these new knee pads do not retain water.
Step 1: Neoprene Mouse Pad
Acquire an inexpensive neoprene mouse pad.
Step 2: Peel
Peel off the mouse pad's fabric cover.
Step 3: Outline
Trace an outline of the stock knee pad on the neoprene.
The stock knee pads are a little shorter than the knee pad pockets on the pants. To take full advantage of the knee pad pockets, extend the length of the trace of the knee pad on the neoprene.
The trace of the knee pad should go from one corner of the neoprene to the other. The resulting knee pad will completely fill the knee pad pocket on the pants.
Step 4: Cut
Cut out the neoprene following the trace line.
Step 5: Insert
Fold the new neoprene knee pad in half and insert it into the knee pad pocket on the pants.
Step 6: Keep
Keep the neoprene scraps for other projects such as my Finger Light.