When I first started trying to learn how to make amigurumi, I struggled with a lot of issues, some chips were stacked against me, others were my own doing. The right tools were the first piece of the puzzle, instruction that made sense to me was the next and yarn was the last.
When I first started out, I bought yarn based on how much it cost and how pretty the color was. I had no idea things like texture, fiber composition and colour were important and would shape my learning experience. The first few balls I bought were Red Heart acrylics, and a few satiny acrylics that were, I think, Bernat. It quickly became apparent, as I struggled with the hook slipping out, popping through the strands or getting stuck in wads of split up weirdness, and the fuzzies that quickly obstructed my view of the loops and stitches I was supposed to see, that this yarn was making things more difficult for me than it had to me. I also found very quickly, that the yarn was drying and sort of roughing up my fingertips, like little SOS pads, and eventually it caused little lifts in the skin that would pull and tear on the yarn. All in all it felt pretty gross tightly clenched in my gnarled up fingertips and I quickly became determined to find something better. That was my experience, yours may be different.
Several attempts with other synthetic yarns later, I fished out an old skein of Bernat Handicrafter Cotton that had been partly used as doll hair on a long forgotten project and tried it out for a change… and thus blossomed my love for amigurumi in 100% cotton.
I find unmercerized kitchen cotton yarn makes the best amis because the yarn doesn’t stretch or give when you work it tight, it doesn’t shred and damage my fingertips (as much anyhow) and it tends to glide along the surfaces of my crochet hooks more fluidly than synthetic yarns. It’s more reasonably priced than wool or other alternative and natural fibers and it’s somewhat readily available (though granted in limited colors). I find texturally different brands and types of worsted weight cotton mesh together better than would different types and brands of synthetic fibers. It is now all that I buy, and the occasional lapse or “I really ought to give this stuff a chance” moment when I am in a colour crunch or see a really great sale on acrylic, quickly serves as a reminder for why I only deal with cotton. All of the amis you see here will be made of kitchen cotton yarns from what is now Spinrite (Bernat Handicrafter Cotton, Lily Sugar & Creme, Peaches & Cream) though most were purchased prior to Spinrite acquiring the two companies and greatly reducing colours so many of my colours are no longer available.
100% cotton does not stretch or give, meaning you can achieve good rigidity in your pieces and sculptural pattern will hold their shape. If the yarn is not mercerized (a process that smoothes the fiber, makes it less likely to shrink when washed and makes the yarn have a glossier, shinier finish), each loop in a stitch is locked into place from the friction of the other loops. The strands don’t slip or slide or shift, meaning the integrity and shape of the stitches and rows hold out well and finished ends woven in are pretty much locked in. I find a fabric made of craft cotton yarn single crochet just seems “beefier”, which while not desirable for say, a sweater, is ideal for amigurumis. Of the few pieces I did finish in acrylic yarn, I was unhappy with how they turned out.
100% cotton (unmercerized) worsted weight yarn is what is best for me, but this is by no means a blanket rule. Generally acrylic or cotton are most common, though some folks do like to use wool. Every hook and every yarn type or brand work differently for different folks, different technique, so if syntho or wool or whatever works better for you, more power to you, run with whatever works. There are no wrong answers, so long as you are happy.