Locate the crack in your Igloo and mark it with a marker if it is very small.
Read the instructions for the canned foam insulation. Open the can and insert the small plastic tube or straw (if the can is equipped with one) into the spray nozzle.
Place the end of the spray nozzle against the crack in the ice chest. Insert the nozzle as far as possible underneath the chipped or broken plastic of the ice chest.
Spray the entire can of foam insulation into the Igloo's crack.
Seal the crack off temporarily with duct tape. Allow the foam insulation to harden and dry according to the instructions on the can.
Remove the duct tape once the foam insulation is dry -- at least 24 to 48 hours.
Mix the J-B Weld on a paper plate and apply it to the crack. Build it up so the sealed area is flush with the plastic on the rest of the ice chest. Allow the J-B Weld to dry according to package instructions.