What thread is used for Flap

These are the two that Hondo uses:

https://www.amazon.com/Madeira-Elastic-Invisible-Knitting--Collars/dp/B01CXCS00O/ref=sr_1_5?ie=UTF8&qid=1469517721&sr=8-5

and also:

https://www.amazon.com/PRYM-977770-Knitting--elastic-transparent/dp/B01AHGJQT2/ref=sr_1_9?ie=UTF8&qid=1469517721&sr=8-9