They are usually sweaty, often dry-clean only, and melt or burn easily if ironed. Indeed, they’re often flammable, and are generally not recommended for children’s wear because of this. Many are derived from fossil fuel byproducts or from highly-polluting chemicals, and are non-biodegradable. They do not have the same warmth as wool of a similar thickness, and, unlike wool, are not usually showerproof without additional chemical coatings.
They are usually cheaper than the wool equivalent, though, so there’s that.
Originally posted on Quora.