Why a bodywarmer?
Your torso loses the most heat, while your arms need freedom of movement. A bodywarmer solves that: warm where it counts, free where it matters. When working with tools, getting in and out of a van, or on scaffolding, you'll immediately notice that sleeves don't get caught on anything.
Padded models with polyester filling are the warmest and keep insulating even when they get damp. Softshell bodywarmers are windproof and stretchy, and fit more snugly under a jacket. Both combine well with a fleece vest underneath.
Certified versions
For work alongside roads or in an environment with flame risk, there are certified bodywarmers: high-visibility bodywarmers to EN ISO 20471 and flame-retardant bodywarmers. Pay attention to the required class here; due to its surface area, a bodywarmer often only reaches class 2.