Chose linen thread over waxed cotton for a 300 page rebind, and I'm still debating myself
Had a customer bring in a beat up 1940s cookbook from her grandma, and I had to pick a sewing thread for the signatures. I went with 18/3 linen over the waxed cotton I usually reach for, mostly because the paper was thin and the cotton felt too bulky in the gutter. Three weeks in and the spine still opens flat, but the knots slip more than I expected and I've had to re-tie two sections already. Curious if anyone here has stuck with linen long term on thin paper or if you'd go back to cotton.