There are many different types of yarns you can use. All types have their advantages and disadvantages. I listed a few (sorted by the alphabet). There are of course also blends and many more types (like Polyester or Polypropylene). These are the ones I have tested:
Acrylic: Acrylic is is resistant to dirt, mildew, moths, and fading. Acrylic is more affordable than wool and is available in a wide range of colors. Sadly it has a tendency to fuzz and shed and is very soft, therefore it doesn’t hold its structure well. Rugs made from acrylic are best in areas that aren’t subjected to too much wear.
Cotton: While cotton carpets are soft and comfortable to walk on, they’re also susceptible to stains and matting.
Nylon: Nylon is known for being one of the strongest and most durable fibers. It’s popularly chosen for its resistance to staining when treated, fading, mold growth, and heat. These characteristics make nylon carpet one of the easiest carpets to clean and maintain.
Wool: Wool is considered a premium fiber as it is resistant to crushing, extremely durable and fire-retardant. Sadly it is also way more expensive than the other choices. If properly cared for wool carpets can last for a long time.
Making a selection is not easy and depends a lot on the money you have available and what you want to do with the rug.
I didn’t like the feel of the nylon rug at all, since it is rather hard. The color choices are also very limited and therefore I am surely not going to use it to make a big rug.
I found tufting cotton to be tricky since it kept on slipping over the scissors and therefore the strand didn’t get cut properly. Even using multiple strands didn’t help. They were all pushed upwards by the scissors and didn’t get cut (apparently they were too smooth and therefore the scissors couldn’t hold on to it). So if you are planning on using cotton, remember to buy really thick yarn and test it first before buying all the yarn you need. Personally, I didn’t like to feel of the finished rug quite as much as the ones made from wool and acrylic.
So after I did some testing I was sure to either use acrylic or wool. They were both a pleasure to work with and I loved the feel of the finished rugs. I ended up using acrylic mainly because it is cheaper and I am still practicing. In the long run, I will probably switch to wool. If I were to make a rug for someone else or if you are planning on selling them, I would probably go with wool. Though I have seen plenty of people selling hand-tufted acrylic rugs.
Unless you are trying to tuft cotton, the thickness of the yarn doesn’t really matter. To get a good and consistent tuft, it is important that there is enough yarn in your gun so that it does not slip out of it. You can archive that with thinner yarn by simply using multiple strands.