Your shoes will be more comfortable than when they were new.
What a great way to start the new year!
I'll demonstrate by resoling a pair of Crocs using contact cement and foam from interlocking floormats.
Until you add tread, the new soles are almost as slippery on wet pavement as the worn-smooth crocs were.
Step 1: Flatten Your Soles
You might want to grind your soles flat with a beltsander or disk sander with the coarsest grit you can find. Instead of flat you could go nuts with amateur orthopedic theories.
My Crocs have worn down pretty flat so I'm going to skip the grinding.
Step 3: Cut out the Soles
Leave a bit extra around the edges.
An electric turkey knife is good for cutting soft foam.
This foam is about the same density as the croc foam.
Step 4: Contact Cement
It's also good for causing headaches, brain damage, and explosions.
Use it somewhere with good ventilation and wear a mask with organic vapor cartridges.
Follow the directions. If you smell this stuff you're doing something wrong.
Step 5: Apply Glue
Paint it on the mating surfaces of the new and old shoes.
If it's glossy at first that's enough. If it runs that's too much.
DON'T PUT THEM TOGETHER YET. WAIT FOR IT TO DRY FIRST!
That's what the directions say, and that's how this stuff works.
If you stick them together wet they'll come apart later and pick up dirt etc.
When it has a matte look to it that's enough.
For a super strong joint I'll drive off all the naptha using ninja tricks before mating them.