I keep reading that it's impossible to block acrylic knits - that it will eventually spring back into its original knitted shape. Then other resources say you can block it by steaming, or "kill" acrylic yarn by ironing it.
I made a swatch of 100% acrylic Red Heart, in preparation for the Stitch-n-Bitch Big Bad Baby Blankent, modified to fit my DD's twin bed. I should've taken a before photo, but trust me, it was less than a perfect square. The seed stitch border warped at a looser gauge than the stockingnette squares that puckered like ribbing at the edges. I thought this to be the perfect time to test the acrylic theory.
The answer is YES, you CAN block acrylic knits. Though it flattens the knitting slightly, the result is a much smoother and softer fabric that now drapes quite nicely.
I used a standard Black and Decker home iron with 3 steam settings and a Teflon surface. The acrylic setting is the lowest temperature, but there's no steam available at that level, so I turned up the iron to the minimum temp setting for steam, in between polyester and cotton blends.
With the steam level set to medium, the swatch directly on the cloth covered ironing board, I took a deep breath, and VERY lightly touched the swatch with the iron, moving it circles, without letting its full weight rest upon the swatch, while slowly pulling the knitting into shape with my other hand. Then when the swatch felt slightly damp, I turned off the steam, and pressed the swatch a little bit more to dry it into shape, while still not letting the full weight of the iron press on it.
Whoever says that you can't block acrylic yarn, apparently never tried this method. This swatch now has perfectly square corners, and after 6 hours, has not crept at all back into its original knitted shape. I've never been a fan of Red Heart acrylic against my skin, but now it's smooth enough to be worthy. The key is not to press too hard, don't let it get too hot, work quickly, pull it into shape a little at a time, and iron it until fully dry. Above all, test your method on a swatch before trying this on a fully knitted project. My next test will be to throw it in the laundry, so I'll let you know tomorrow....