"Minimal yet durable, boasting just enough storage to get you through a long race without weighing you down." - Outside Online
This is the vest you need for OCR because it's made of a very durable, nylon rip-stop fabric that holds up to the abuse of water, mud, and abrasion against walls, the ground, and other hazards along the course.
It's also a perfect training vest because it has enough capacity to carry hydration along with extra clothes and food.