How to make a duct tape cast for knee braces

This is the written tutorial companion for the video posted here: https://youtu.be/yUcN_vSVzH4

Things you’ll need

Before you begin, assemble the materials you will need:

• permanent markers (in a few colours if you have them; one is fine otherwise),
• ruler,
• duct tape,
• plastic wrap,
• scissors (preferably blunt-tipped but sharp),
• several elastic bands large enough to go around your leg,
• and a helper to do the taping

Before starting the duct-taping process

• Wrap the area you’re going to be taping in plastic wrap, covering at least 15+ centimetres above and below the kneecap to be safe.  If the plastic wrap won’t stay up by itself, you might want to use elastic bands or clear tape to keep it in place while you’re working.

• You should only need to tape one leg.  If you only need one knee brace, tape the side that needs it.  If you need both knees supported, pick your dominant leg.  Please remember to label the duct tape cast with either “RIGHT” or “LEFT”, depending on which leg you taped.

• Make sure that you’re standing with your weight distributed between your legs, and try to stand the way you usually do.  Don’t bend or lock your knees unless that’s your normal posture.  When it’s time to draw the marking lines, try to stand just the way you regularly stand.

Photo illustrations

Creating the duct tape cast

• Using short strips of duct tape, tape over the area you want your knee brace to cover, plus a bit extra for easier marking later on – at least a few centimetres above and below the finished brace length.  Try your best to follow the contours of the knee and leg with minimum distortion.  The video tutorial will be helpful if you’ve never done this sort of thing before.

• When going over more pronounced curves and bumps, use shorter pieces of tape.

• Try not to bend your knee sharply or move in any way that makes the duct tape distort or pull while you’re marking, or it can throw out the pattern.

• Don’t pull the tape so tight that it changes the shape of your soft tissues.  Make sure you’re not squeezing or making significant dents in your skin, or the finished brace might end up too tight. 

• On the other hand, don’t tape so loosely that there’s any space between your body and the tape, or so it slides around on you, or the finished brace will be too big.  You shouldn’t be able to insert a finger between you and the tape at any point without stretching the tape.

• Don’t leave any un-taped areas.  However, try not to use more than two or at most three layers of duct tape anywhere, or the finished cast might get too stiff to flatten accurately for a pattern.

• If the cast in progress tries to slide down (which it probably will!), consider temporarily taping it to your body with some clear tape or even a small piece of duct tape if you think it won’t irritate your skin.  It’s critical that the half-finished mold doesn’t travel down on your leg or shift around, especially once you start marking.

• When your helper finishes taping, make sure you take a good look to make sure there aren’t any missed spots, and double-check that the duct tape cast hasn’t slid down at all on you.  Once you’re sure, you can start the really important part: the marking!

Marking your duct tape cast

• Draw several arrows at several places to show which way points up.

• While you’re standing as normally as you can, have your helper slide elastic bands onto the duct tape cast and place them on the following areas (refer to photo):
  1. at the top where you want the top edge of the knee brace to sit,
  2. just above your knee joint,
  3. just below your knee joint (just let it settle where it wants to as close to are bit under the kneecap as is reasonable – your knee continues to stick out past the patella, so you’ll need to go below the bump of the whole joint) and
  4. where you want the bottom of your knee brace to sit.  It’s okay if the elastic bands are not perfectly horizontal, but do try to position them to be as level with the ground as possible. 

• The exact desired length of your knee brace is up to you, but about 12 cm above and below your kneecap is a decent default length if you don’t have a personal preference.  The distance between your top two elastics will be the basis for the height/width (depending on how you think of it) of your top lace-up band, and the distance between your bottom two elastics, your bottom band.  Refer to the photo if this seems unclear.

• Keep in mind that your lower lace-up band should never go past the widest part of your calf, or it won’t work properly!

• Draw around each elastic band with a permanent marker.  You’re basically drawing on the placement of the lace-up bands in your future knee brace.

• Optionally, cross-hatch to mark out the areas above the top line and below the bottom line to remind yourself to trim off the extra tape later.

• Now, draw CAREFULLY around your kneecap.  It’s very important to get the size and placement as accurate as possible, or the patella ring will end up the wrong size or in the wrong place!  Take your time and check yet again to make sure that the duct tape cast hasn’t slipped down while you’re doing this.

• Double-check the relative placement of your lines and your kneecap outline, and make sure everything is in the right location.  If you need to re-draw any lines, cross out the old line to make sure there’s no confusion, and maybe use a different colour of marker to draw in the new lines, if you have one.

• Holding your ruler perpendicular to the ground, draw a line down the centre front.  Make sure that the line bisects your kneecap circle as accurately as possible, and that the line is at 90 degrees to the floor.  Label the line “CF” for centre front.

• Now draw a centre back line with the ruler at 90 degrees to the floor.  Try to get the line as close to the middle of the back of your leg as you can while still keeping it perpendicular to the ground.  Label it “CB” for centre back.

• Draw over the area at the back of your knee where the duct tape bunches up the most when you slightly bend your knee.  This will become the cut-out “window” behind your knee in the finished brace.  For most of us, this will be a horizontal fish-eye shape, but don’t worry too much about the exact shape; just try to generally indicate the area of maximum bunching.

• Next, draw a line down the inside and outside of the knee, keeping the ruler perpendicular to the floor and trying to evenly divide your leg front to back (these would be the side seams of the knee sleeve).  Many legs won’t divide evenly all the way up and down, though; if that’s the case for you, try to bisect your body (front to back) at kneecap level and keep the ruler 90 degrees to the ground, and don’t worry about getting the rest of the leg to divide evenly.  Label these lines “OUTER” and “INNER.”

• If you haven’t already, write either LEFT or RIGHT on the duct tape depending on which leg you taped. 

Taking reference photos

After checking that you’ve made all the necessary marks, take a few photos of your taped leg, just in case it’s needed for reference later on.

Cutting off and trimming the duct tape cast

• Cut the duct tape off very, VERY carefully, following one of the vertical lines.  We chose to cut on the outer leg line. It’s easy to nick the tape-ee, and even easier for the helper to cut their own fingers, while doing this.  Take your time, go as slowly as you need to, and be safe – and try to avoid pulling on or distorting the tape while you work.  It might be safest to try to keep the helper’s hand between the tape and the skin while cutting the tape (but watch those fingers!).

• Once the duct tape cast is safely off the body, trim off the excess tape above and below the top and bottom lines, leaving only the portion that will become the actual knee brace pattern.

Once you’re finished

Handle the finished cast gently to prevent it from changing shape or stretching out as much as possible.  Roll it up loosely for mailing rather than making sharp folds.