Acrylic yarn is made from synthetic polymer fiber rather than either plant or animal based fibers that are grown and harvested. First produced by DuPont in 1941 and sold under the brand name 'Orlon', acrylic yarns have become one of the most popular textile materials on the market - especially when it comes to creating blends!
Synthetic fibers are often manufactured to mimic the qualities of natural sheep wool, emphasizing softness, warmth and lightness (though virtually any qualities are possible with the right tweaking). They're also very simple to clean and almost almost washing machine friendly, making them much more attractive for everyday wear clothing than many natural fibers. Consumers also often enjoy a significant cost advantage when buying acrylics because the manufacturers do not have to contend with pest control problems (polymer fibers are indigestible to moths) and can produce the material in large quantities all year round.
The clear drawback the acrylics is that sometimes (though certainly not always), because it is simply trying to imitate a natural fiber, it can look and feel - for lack of a better word - like plastic. Poorly manufactured synthetic yarns are much more common than well crafted ones, and they look the part of being a lesser thread aspiring to something grander. This drawback is why many companies choose to use acrylics as simply a blend, bolstering the rich beauty of natural fibers so that they can be machine washed and can be sold at a better price.
We encourage you not to shy away from a yarn just because it says 'acrylic' somewhere on the band. Yes, there are a lot of terrible acrylics out there - but there are also plenty of great acrylics on the market today, and some blends are among the best yarns you could ever hope to come across.