Arachodus

(also known as spidertooth fiber)
Not to be confused with spider silk. Spiderwolf teeth are incredibly stiff and hard, with absurd levels of tensile strength. Denizens of the Darklit Cities have devised a method of drawing out these teeth into fibers. This material is used for various applications where a modern material such as aramid or carbon fiber would be appropriate, as it exhibits both the stiffness and impact/wear resistance that both are known for (and the elongation of break of aramids). As one would expect, the material is also very hard- almost approaching tungsten.
The downside is production cost: an average bonespider only generates around 4-5 cm2 of light ~200gsm fabric. Trade from the midlands is an inconsistent source at best due to historically poor relations between the regions, and the resulting material is generally considered to be inferior quality. The process itself is not particularly demanding or lengthy, although like most things the Cotd do, it has been perfected to a precise art.
Armor made primarily from spidertooth is rare due to its prohibitive cost, but small amounts of the material are often added into cloth weaves to dramatically improve cutting resistance. Strictly speaking, arachodus is created by magically forcing plastic deformation on spiderwolf teeth- there's no reason that it couldn't be made into things other than threads, just that thread is the most efficient use of the material. Solid arachodus plate armor is entirely possible, but impossibly expensive.
Common grades of spidertooth cloth are sparse (~5%), (~20%), and heavy (~50%). Pure spidertooth cloth is very rarely seen.
Note that arachodus technically only refers to fiber drawn from a bonespider's fangs. Other spiderwolf species tend to have lesser mechanical properties, although not by a significant margin (around 10% worse in most cases). Bonespider-based fiber is a vaguely iridescent and oily gray-yellow, while most spiderwolf fangs are ivory in color.