For anyone else that isn't an engineer and also doesn't know, toughness is a defined term in material science.
Toughness is the ability of a material to absorb energy and plastically deform without fracturing. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. It is also defined as a material's resistance to fracture when stressed.
Sounds like it'd work better than kevlar for armor.
I thought the article was being lazy by saying "tougher" but TIL that's the scientific term.