Hut Slippers

Looking good. It appears that you are using evazote closed cell foam which is relatively heavy as far as CCF goes but it also is more durable. Evazote is probably a good choice for this type of application, but if you're looking to save weight then regular ccf weighs ~60% as much but it probably wouldn't last as long in this application and I don't know if you can get it this thin.

Duct tape is surprisingly heavy stuff. Packing tape is a lot lighter but again, it's less durable too. Even duct tape may start to peel apart over time in this application though. Just today I noticed a lot of peeling on my duct tape/bubble wrap camera case. Do you have a weight breakdown on how much of the weight is the foam and how much is the tape?

If you really want to get fancy, you could use other materials for the uppers like nylon or cuben. You probably wouldn't want any light fabric on the sole of your slippers. One way to attach cuben would be to use a knife/hotknife and get a horizontal slit around the perimeter of the foam. Then you could glue the cuben upper into the slit. SeamGrip and nylon would probably work well for a simple trial run and the difference is likely only a couple grams.

It might be nice to incorporate some way of keeping your feet cleaner while wearing these, so a midnight pee run doesn't leave you with dirty feet. Enclosing the toe area and adding a ledge around the rest of the slipper should do the trick.