You know, it's funny that you brought this up. Many years ago I attempted to grow luffa sponges. I was intent on the idea of harvesting and cleaning the sponges, then setting them in molds, according to their size, and casting them full of homemade artisan
soap. Once set, I would then cut the luffa into slices, and inch and a half to two inches thick to be used as
shower soaps that would exfoliate one's skin while you bath with it.
Unfortunately, having no way to know what I was doing, I failed miserably. Perhaps I could have learned something from a library, but it probably didn't occur to me at the time that somewhere there might be information useful to me. This was probably around 1980 and there certainly wasn't any kind of internet then.
Maybe it's time to revisit this idea? I don't however, believe these veggies will perform like a real sponge.