These bobbins are made using high strength, high tenacity poyester 70D/2 thread. Don't be fooled by cheap prewound bobbins that use lower quality regular tenacity thread when comparing brands. There is a difference. High tenacity thread resists breaking and run great at high stitch speeds. Spend more time embroidering instead of correcting thread breaks. 150 yards of 70D/2 high tenacity filament polyester thread each.