I have heard white vinegar gets fold lines out, it also sets creases. I mix it with water in a spray bottle to set creases with the iron. Sometimes the creases stay after washing, sometimes not; depends on the fabric, too, I'd guess.

Mary L

I've white vinegar straight & applied it with a cheap paint brush to stubborn parts.

Here's a tip I've used w/ some success - wet strips of brown kraft paper (paper grocery sacks), lay over crease & iron until dry.You can do this to set creases too.

I think tannic acid in the brown paper is what does it.

& you also might also want to change the way you're storing these items, so they don't get creased too much...?

HTH