Narrow Elastic-- around 1/4"
3/16" (5mm) elastic or just over 1/4" (7mm) Sold by the yard or in preset quantities.
The soft elastic is doesn't have a lot of memory but is much softer than the braided option. Best for applications where it won't be over-stretched. Works well for around the ear masks since it is soft.
If you want a stiffer elastic with more memory choose the braided version in 3/16"