Most dog hoodie suppliers describe fabric the way a pet store description does | "cozy," "soft," "premium." None of that tells you whether the hoodie will overheat a dog on a mild day, pill after five washes, or hold its shape for a season. French terry and fleece are both knit on the same machines and start as the same loop structure; the difference is whether that loop gets brushed into a fuzzy nap afterward. That one step changes warmth, breathability, durability, and how the fabric takes print or embroidery.
The second common failure is the harness hole. A hole cut in the wrong spot, or without reinforcement, becomes a stress point | every step the dog takes pulls the surrounding fabric toward the leash direction, and the hoodie twists, ripples, or slides off-centre over the course of a walk. This is a pattern and construction detail, not a fabric choice, and it's the difference between a hoodie that works for daily walks and one that only works for photos.