Wait! Wait!
Rubberized horse-hair is exactly that. I have regular horsehair and rubberized. 40 years ago it was used to stuff sofas and stiffed chairs.
I can give you two sources. 4D Modelshop in London has it. Also, I traded some USA beef jerky to a Dutch soldier for some rubberized horsehair that they wrap around their artillery shells.
The rubberized horsehair looks just like the bocage undergrowth of France. You can't replicate it with anything else I have seen. That darn book is so great that I have had to scrouge a number of things they mention, that you can't get in the USA, like silver birch catkin tree seeds to use as leaves (see my "Super-Tree" article), flex-i-bark, and some other items, like the rubberized horse-hair.
Good luck. The folks at 4D have a lot of great stuff for modelers, including brass stencils now.
Sealhead