Single or double fold? This is a matter of taste, what you prefer
Single fold – Folds the binding tree times, leaving a “raw” edge on the back. Normally the seam cover this on the back. Gives nice and thin binding edge. Suitable for clothes adult and kids. Easy to attach snap buttons.
Double fold – Folds the binding four times, looks the same on both sides. Nice on blankets and other projects. A thicker edge than the single fold and can be a bit harder to attach snap buttons.
Not sure what size to get?
Depends on what you are planning to sew. What width you want on the finished binding.
My personal favourite and bestseller are the single fold 35 mm. A good allround size for both baby, kids and adult.
Next favourite are the wide 50mm single fold, a finished size of 2cm!