For TPU hair band, we usually take semi-perimeter instead of diameter as one of measurement index of size. TPU clear elastic hair tie is stink-proof and can be recycled. We have TPU clear band in two classes of quality. The higher quality one is anti-yellowing and anti-aging. If you put the hair tie under sunlight, you will find it still there in 2 month. But some low quality rubber hair band will be break in 2 weeks.
TPU band in semi-perimeter of 25 mm or 30 mm is common. That in 15 mm will be used for children.