Do techniques for stretching shoes only work with genuine leather or suede? Will man-made materials stretch?

I'm trying to decide right now whether to keep or donate these shoes as I plan on making a haul to the goodwill later. I like the way they look but wish they were a 1/2 size bigger. I decide to do Angie's wet feet trick but then thought maybe won't work with material.

Should I keep or pass? Thanks for any input!

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