This instructable takes a huge chunk of inspiration from a pre existing lightweight rear mudguard that is already commercially available. I have adapted the design slightly and, in addition, created a small guard for the front wheel.
These mudguards are small enough to keep in the bottom of your bag for whenever you may need them AND this whole instructable cost me only £1!!!
Step 1: Find your material!
You need to find a suitable plastic material with which to build your mudguard. I considered using the thin plastic sheeting that document folders are constructed from however i decided it could end up being a little flimsy. I found this multi pack of flexible kitchen cutting boards in a super market for £3. The material that they are made from is flexible, strong and light. A single cutting board will be enough to make both front and rear mudguards.
Step 2: Mark out the rear mudguard
I managed to source the outline of another popular lightweight mudguard and used this as a starting point. I lengthened the design slightly. The final stencil will be uploaded in the final step of this instructable. I used a Stanley knife to make the cuts although you can get away with using scissors.
Step 3: Hole punch and score
I used a normal hole punch to make the holes and then realised that I should have just used a normal drill bit as the holes need to be quite a bit bigger. These holes will clip onto the underside of your saddle.
I chose to score a line down the middle of the mudguard on the top side. This scored line will allow the plastic to flex upwards much like a conventional mudguard.
Step 4: Mark out and cut the front mudguard
There should just be enough material left to create the front mudguard. I used a very similar design as the rear guard. As there isn't anywhere useful on the front forks to attach this one to you'll have to use a rubber band to strap it to the underside of the bike frame.
Make two holes and link them with a single slit. The rubber band will loop through these holes and over the frame.