I've used spray starch on my hakama (poly-cotton) when ironing it after washing.
It kind of worked in that the pleats stayed crisper for a bit longer, but eventually they came out again. I also found I was having to wash it more because folding it up after class when it was all sweaty just led to it smelling quite quickly
Nowadays I'm onto my third 2nd hand polycotton hakama, and the pleats are all over the place, so I don't fold it properly after class, I just roll it loosely then as soon as I get home I hang it up to air.
It doesn't look any worse than if it had been folded, and doesn't need washing so often, so I'm not freaking out about it
As the knees are starting to give way, I'll have to buy a new one at some stage next year (yay my first ever new hakama
) but will go for one with pre-stitched pleats so I can find them again after washing it!
Ruth