Ok so this is going to be a rather short instructable as these DIY knee pads are very impractical to build unless you already have the materials at hand or can obtain them for little to no money. If you were to buy the materials new they would probably cost much more than a decent set of pads(Disclaimer: I have not checked prices). But in terms of quality and design these came out much better than I had hoped, and only took about 3 hrs to build.

I Made these because a just got into longboarding and want to save my knees/pants, but dont have alot of extra money to spend. so here yah go.

Step 1: Tools and Materials

You will need

Materials

3/4 in s40 PVC pipe (about 1 to 2ft)
One foam yoga mat( about 3mm thick) I paid $2.00
One Eva foam shop mat(about 10mm) I paid $0.25
One set of shoe laces
Velcro(I recycled mine from old wornout pads)
Synthetic straps

Tools

Heat gun
Pipe cutter
Belt sander
Dremel
Gloves
Scissors
2x 2x4's
Sowing machine
Drill

Step 2: Shaping the Guards

To start, take your PVC pipe and cut two length's as wide as you want your pads, then cut a straight line down the center of the pipes with your Dremel.

Once you have done this you can start heating the pipe with a heat gun(Be careful not to burn it), once it has softened put on your gloves, and pry it apart, then flatten it between the 2x4's. After it has cooled take it out and flatten and round the edges on a belt sander. Then heat it again(not as long this time) then press it over the 2x4 to achieve a slightly rounded shape. you now have your plastic guards

Step 3: Putting It Together

Now cut your foam to the desired size and shape and sandwich it all together in this order(from the top) Guards, EVA Foam, Yoga Mat. Then Drill eight holes around the edges of the guard in a 2x pattern. Then Run The shoe laces though the holes to secure it all together(optional: you can also drill a set of holes above and below the guard aswell) once you have done this sew on the vertical and horizontal straps and Velcro.