Cloth is the new plate armor.
I think I just figured out why this is. Check the material_template_default raw -> thread_plant_template (near the end). Shear_yield and shear_fracture are both set to 600,000. These values are used in combat calculations for edged weapons, and Toady said he used tensile strength (in kPa) for them.
As comparison, metals have all these set to 520,000(yield) and 860,000(fracture) (Toady got these values from stainless steel) and wood is set to 40,000 (from pine, says the Toad). Therefore, any plant cloth is harder to cut through than steel! Density plays a part, but this is a very big influence (see Nimbo's research). As teeth and claws are edged/pointed attacks for animals, these numbers affect them as well. I would recommend changing the values something a bit higher than human skin (20,000), such as 30,000.
Silk is set to 1,150,000 and 1,200,000 (!), so I recommend toning that down as well, perhaps to 40,000 (same as wood). I don't dispute that these are accurate tensile strengths, though I haven't looked up most of them, but their values are just not functional in the combat calculations currently in use.
EDIT: Leather has these values set to 25,000, so that may need some rebalancing as well.
Material properties can get really weird when they are non-homogeneous. There needs to either be a lot of tweaking or many special cases for different materials.
Goat silk... where do they extrude it?
The mammaries as I recall, mixed in with the milk. Which lead to further problems when it was discovered that the
method of extraction(specifically, the shape of the orifice and gland that the silk is drawn from) has a profound impact on its strength(read as "it kind of works in the lab").