metal / plastic hybrid pot

Metal/plastic hybrid – you mean beer cans??  :)

You can boil in plastic or paper bags.  Try an image search on either. The risk in these is of course springing a leak, and what every toxic compounds may leech in to your water when heated.

While this could save you some weight on your pot, you add it back with whatever is needed to support the flimsy material.  Also, if it’s so fragile that you need a spare, that has to be included in the weight as well.

I tried boiling in parchment paper (several pieces are still way lighter than a beer can) but they always sprung a leak.  As the water approaches boiling, small bubbles form on the bottom which insulate the paper from the water, so the paper heats, singes and creates a leak.

Not sure how much weight or not it would save, but if you’re going this route, look into silicone pouches. Pretty durable, fairly heat resistant, and very, very little leaching.

I don’t know about extending a pot. But I did make a floating silicone lid recently by cutting up a silicone baking mat. I haven’t tried it in the backcountry yet but so far I really like the concept. Unlike other UL lids it’s unlikely to blow off because it’s below the lip of the pot and the surface tension holds it on there. It’s also easier to tell when the water is boiling than with any other lid I’ve used. And fun to watch the patterns as it nears boiling.

You can fish it out with a spoon and it cools off enough to touch in a few seconds, so no need to add a handle.

If you go through with your idea, I would definitely go silicone instead of plastic if you can. It’s food safe, and heat safe up to 400 degrees or so.

If the plastic/silicone is thick enough not to collapse it may not be as light as Ti or particularly the like of a beer can.
otherwise I see a great potential for an accident to happen.

Sea2Summit do a series of metal/silicone pots :

http://www.seatosummit.com.au/product-category/outdoor/x-series/

the advantage there is saving space (not for me because I fill my pot with stuff) not the weight.

I have seen another brand locally but I think it is a house brand , not sure.

(no, it was another S2S , part of a set)