For rainy outdoor racing, carbon fiber is usually the best choice for the frame itself, but the real answer depends on how wet, rough, and crash-prone the course is. Carbon does not rust, it stays very stiff, and that stiffness helps keep the quad feeling precise in fast cornering and punch-outs. In wet races, that crisp handling can matter more than anything else because grip is already inconsistent and you want the frame to respond exactly the way you expect. If you are running a race setup with locked-in tuning, carbon also tends to hold that tuning better than a softer material.
That said, carbon is not perfect. Wet conditions often mean more crashes, more dirty landings, and more chance of hard impacts with muddy ground, fences, or tree roots. Carbon handles normal racing abuse well, but when it fails, it can crack suddenly instead of bending. If you race in places where you expect repeated hits or awkward recoveries in wet grass, you need to think about frame thickness and arm design just as much as the material. A 5 mm or thicker carbon arm can be a lot more forgiving than a thin lightweight one, and a replaceable-arm design is a smart move because one broken arm is easier to swap than rebuilding the entire frame.
Aluminum is usually not my first pick for a race quad in the rain. It will not rust quickly in the way steel does, but it can oxidize, it can bend, and once it bends your geometry is off. That is bad for racing because even a slightly twisted frame changes how the quad tracks through gates and corners. Aluminum can make sense for certain camera cages, standoffs, or custom parts, but for the main racing frame it is generally less popular than carbon.
Plastic or nylon-based frames are the most forgiving in crashes, but they are usually too flexible for serious racing unless you are talking about smaller freestyle builds or very beginner-friendly rigs. In wet conditions, that extra flex can make the quad feel sloppy. Water itself is not usually the reason to choose plastic; crash resistance is.
The bigger issue in rain is not just the frame material. Motors, bearings, electronics, and fasteners matter at least as much. Stainless hardware, sealed bearings if possible, conformal coating on the electronics, and careful drying after each session will do more for reliability than switching from one frame material to another. If you want the best all-around race choice for rainy outdoor events, I would pick a quality carbon fiber frame with replaceable arms, then focus on weatherproofing the rest of the build. If you want, I can also suggest a rain-ready parts list for the whole quad.
