Steaming and ironing aren't substitutes for each other, unfortunately.
Steaming is great for blocking, removing wrinkles and freshening fabrics (especially wool) so they look loftier and fluffier. The hot steam does the work; the steamer doesn't press down on the fabric.
Ironing works by direct contact of a hot metal plate on the fabric. It flattens out the fabric to remove wrinkles and gives it a smooth, shiny finish. It can also iron in pleats, smooth seams and hems, etc. A steam iron can do both steam-pressing and ironing, obviously, but it can't produce the volume of steam that a steamer can.
A steamer isn't a good substitute for an iron if you need to do shirts, crisp cottons or linens. I used to think that a heavy iron was necessary for fast, smooth ironing, but I was wrong The one I have now is very lightweight and doesn't bother my wrist nearly as much as the old one. It's an inexpensive Black & Decker, but I'm sure there are even better, more ergonomically correct ones out there.
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