To reiterate what I've taught and been taught, when you are binding books you generally need a thread that will not stretch or break
Irish Linen Bookbinding Thread 18/3 - 10 yards or full spool - WNY Book Arts Center
Known for its strength, durability, and beautiful sheen, flax linen has been bookbinders’ preferred thread fiber for centuries. Colophon's Best line
Colophon's Best Linen Thread — Colophon Book Arts Supply
Colophon's Best Linen Thread — Colophon Book Arts Supply
Needle and Thread – DAS Bookbinding
bookbinding thread – Peachey Conservation
File:Bookbinding tie thread 2.jpg - Wikimedia Commons
Thread for Bookbinding and More
SEWING THREAD – Silk and linen for special projects - SARTOR BOHEMIA
Jmuiiu 10 Colors Leather Thread - Waxed Thread Cord, Leather Thread, Waxed Thread for Bracelets, Jewelry Making, Bookbinding, Leather Repair
A Guide To The Types Of Bookbinding, Handy Design Tips
The Wandering Bookbinder
DIY Tutorial: How to Choose the Right Bookbinding Thread
100% cotton thread, reel with 1000 meters. ideal for sewing 90 gr paper booklets such as Cultural paper or bond paper. Hilo de Algodón Black