Generally, you do not need to size up your jacket when wearing the 509 R-Mor Protection Vest. The vest is designed to be low-profile and fit comfortably under your existing outerwear without adding significant bulk1.
However, if your jacket is already a snug fit, you might want to consider trying it on with the vest to ensure you have enough room for comfortable movement. The vest features stretchable materials and adjustable sides, which help it conform to your body and fit seamlessly under your jacket1.
If you’re between sizes or prefer a looser fit, sizing up your jacket could provide extra comfort, especially if you plan to wear additional layers underneath.