It's been brought up already, but the
Star Wars: The Last Jedi - Visual Dictionary is worth the ~$15. Here's a quote:
"The layered armor of the Praetorian Guard is a high-tech onion-skin of laminate, impregnated with conductive wirepaths that, once powered, create an intense local magnetic field. Once this energy-intensive field activates, the powered plates can deflect blaster fire. Even a lightsaber will glance off, though a directed thrust will penetrate the shell."
The Praetorian Guard's fighting style is comprised of Teras Kasi, Bakuuni Hand, (unarmed) Enchani, and Nar Kanji. Without knowing anything specific about the other styles, I know that
Teras Kasi was developed to counter/fight Jedi.