When any object goes through the air, a thin cushion of air wraps around it that stays relatively still. This boundary layer is why you get dust trapped on your ceiling fan. At slower speeds, the air around a soccer ball moves smoothly over the surface and separates off the sides of the ball at its widest points. Imagine a ball moving from right to left across a clock, Goff explains, so traveling from the 3 to the 9. With laminar flow, the air flows over the surface and then flows off at the 12 and 6, which creates more drag in the air. Drag slows the ball down faster. At higher speeds, the air moves turbulently across the ball’s surface and peels off at the 2 and 4. The wind effectively wraps around the back. This turbulent flow has less drag, which means the ball keeps moving at high speed for longer.
Only size 5, and size 4 are available for this. Although this should not be a major problem as this is for recreational play and practicing purpose, so kids are ok to play with this as well. In fact, the ball that will be given away to the developing countries will be used by the kids mostly. If you are buying this for an adult go for size 5, and if you are buying for kids or youth players then better go for size 4.
On the other hand, replicas (sometimes called training balls or gliders) are designed to be just like the official match balls but are much cheaper. Their panels are often stitched rather than thermally-bonded and are made of a different material. However, they’re not necessarily less durable than official match balls. So, they’re the recommended option for most players. https://www.youtube.com/watch?v=j2Xn84L3Kcs