I am in a practice of equipping leathers for battle vs. blunt-weapon assailants. I feel, after some semi-scientific arena testing that the benefits of added speed are crucial, given that blunt damage mostly negates the value of armours, with the possible exception of steel and adamantium; However, to be sure, let's take a look at how DF describes the material.
Don't worry - I've clipped some of the extraneous data from the template.
[MATERIAL_TEMPLATE:LEATHER_TEMPLATE]
[SOLID_DENSITY:500]
[IMPACT_YIELD:10000]
[IMPACT_FRACTURE:10000]
[IMPACT_STRAIN_AT_YIELD:50000]
[COMPRESSIVE_YIELD:10000]
[COMPRESSIVE_FRACTURE:10000]
[COMPRESSIVE_STRAIN_AT_YIELD:50000]
[TENSILE_YIELD:10000]
[TENSILE_FRACTURE:10000]
[TENSILE_STRAIN_AT_YIELD:50000]
[TORSION_YIELD:10000]
[TORSION_FRACTURE:10000]
[TORSION_STRAIN_AT_YIELD:50000]
[SHEAR_YIELD:25000] -- was 15 to 37 MPa in animal byproducts net pdf
[SHEAR_FRACTURE:25000]
[SHEAR_STRAIN_AT_YIELD:50000]
[BENDING_YIELD:10000]
[BENDING_FRACTURE:10000]
[BENDING_STRAIN_AT_YIELD:50000]
[MAX_EDGE:0]
[ABSORPTION:40]
I've added this to the material comparison chart on the weapons page of the wiki.
http://dwarffortresswiki.org/index.php/DF2012:Weapon#Weapon_Material_QualityThe numbers suggest that it is (go figure) like wearing an extra layer of skin. Which ain't all bad. It's certainly better than the values we get for silk and cloth.
But this is strictly examining the [LEATHER] material entry...
When we refer to the raw descriptions of items like coats, tunics and trousers, there is another tag: [STRUCTURAL_ELASTICITY_WOVEN_THREAD]. This suggests that 'clothing' offers rather poor protective value. Or maybe it means that it does little to hamper movement? In any case, we also see that these objects are [SOFT] - which may have combat implications, but seems mostly to be a determinant to which materials can be used in its construction.