Though I'd been thinking of them for a while, I did these liners on the spur of the moment so I just used whatever I had lying around. I am a squirrel though, it must be said, so what I have "lying around" you may well have to go shopping for.
They came out brilliantly though; soft, comfy and warm; and only took an hour including time spent scrounging round for materials so if you gather everything together before you start, you could be done in about 45mins. So don't ditch the boots just because the inners have come away (or completely fall out like mine did) knock up a pair of these to proudly display to your nearest and dearest...preferably before you wear them...or better yet, take a picture!
Step 1: Gather Your Gear
What you'll need:
Your boot insoles
Felt fabric in your colour of choice (enough to make two layers each for both feet)
Craft foam, again in whatever colour you like, enough for one layer per foot
scissors, pen, glue (fabric/pva/bostic etc)
Needle and strong thread.