With clean carded wool that looks a bit like fibreglass insulation I pull off thin strips to wind around the wire armatures. Then stab stab stab with a barbed needle to push the outer fibres inward where they grab onto the insides. Then add more wool and keep sculpting. The more I stab the firmer the piece gets.
I'm learning this art form from artist Sara Renzulli who provides fun and free tutorials on her website. Most of these creatures start out as her designs but each one turns out quite differently than those of others following the same tutorials. I have been needle felting sporadically for 2 years.
Here is a fox from start to finish.
First the raw materials.