A paddle brush and a round brush serve different purposes in hair styling and have distinct designs. 
A paddle brush is flat, wide, and rectangular or oval-shaped, with a large surface area. It is designed for detangling, smoothing, and straightening hair. The bristles are typically set in a cushioned base, which helps reduce static and frizz while providing a gentle brushing experience. Paddle brushes are ideal for long, straight, or thick hair, as they cover more area and can efficiently detangle without causing breakage. They are also useful for blow-drying hair straight, as they help flatten the hair cuticle, resulting in a sleek finish.
In contrast, a round brush is cylindrical and comes in various diameters, which influence the type of curl or volume achieved. The bristles are arranged around the barrel, which can be made of materials like ceramic, metal, or wood. Round brushes are primarily used for styling and adding volume, curls, or waves to the hair. They are essential for blow-drying techniques that require lifting the roots and creating body. The smaller the barrel, the tighter the curl; larger barrels are used for creating loose waves or adding volume to the roots. Round brushes are versatile and suitable for various hair types, but they require more skill to use effectively, especially when combined with a blow dryer.
In summary, paddle brushes are best for detangling and straightening, while round brushes are ideal for styling, adding volume, and creating curls or waves.