Well, panels are not any different component. Panels are the segments or octagon quilt that are seen outside the balls. Of course, nowadays you will find some other shapes besides octagon. FIFA official balls usually contain 32 panels. But nowadays you will also find 26, 18, 14, 8 or even 6 panels with different shapes and designs from those of conventional balls.
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