Sequins on a knit fabric backing
These are fabrics that still have stretch to them, so they could be lightweight single jersey like T shirt fabric. The edges won’t fray so you could leave it unhemmed.
Sequins on a mesh fabric backing
Sometimes these fabrics still have stretch in them but they are mainly netting or tulle fabrics with the sequins sewn onto them in rows or a pattern. These will not fray either so could be left unhemmed too.
Sequins on a woven backing fabric
Woven fabrics include organza, taffeta, viscose rayon and many others. These fabrics do not have any stretch in them in either direction and are therefore very stable to work with. However they can fray considerably so will need careful consideration with seam finishes and hems.
Sequins on Lace
Lace fabrics are often decorated with sequins to accentuate the design of the lace itself. They can be both stretch and non stretch so it is a good idea to check so you know whether they will fray or not.
Sequins themselves can be sewn or glued onto fabric. The stitched sequins can be sewn in patterns or haphazardly which is also described as “all-over sequins”. They can be sewn flat to the fabric or just over one side of the sequin disc so it can lift up away from the fabric. These are also known as paliettes. Sequins themselves can be a variety of shapes and sizes, circular, oval, teardrop and some even cupped or crimped.