Start with your base layer
A base layer is the foundation of every winter outfit. It should sit close to the skin with no bunching at the armhole. When you try a base layer on, check how it feels at the armpit and the sides of your chest. If fabric gathers or pulls at any point, that layer will create friction once you add a mid layer on top. The armhole is especially important because it is the most active area of the upper body.
Try layers over the thinnest shirt you actually wear in winter, not over a heavy sweater. Wearing a thick shirt underneath makes every layer look and feel like it fits better than it does. A thin cotton or wool blend shirt gives you a realistic sense of how much room you have in each piece. If the fit is tight over a thin shirt, it will be even tighter once you add another layer.
If you notice static cling on a synthetic base layer, that is a sign of dry fabric. A cotton or wool blend reduces static and feels more comfortable against your skin. Static also makes layers stick together, which can shift the fit as you move. Test the fabric by rubbing it against your forearm. If it clings tightly, look for a blend instead.
Check your mid layer for shoulder bulk
The mid layer is where most people go wrong. A mid layer that adds bulk at the shoulder seam is too thick for that jacket. When you slip your arms into the mid layer and then reach for the jacket, notice whether the shoulder area feels compressed or tight. If the jacket struggles to sit smoothly over the mid layer shoulders, the combination will not work in real life.
Move your arms while wearing both layers. Lift them to the side, cross them in front of you, and reach behind your back. A mid layer that looks fine while standing can feel restrictive once you bend or stretch. The shoulder seam is the first place to watch for strain. If the fabric digs into your shoulder when you reach up, the mid layer is too thick for ... (line truncated to 2000 chars)