They are made of Moso bamboo which is the largest and strongest bamboo out of over 1,000 different species. The patina finish is obtained with thermal heat.
Sizes US 0 (2mm) through US 2 (2.75mm) come with six needles per set. Sizes US 3 (3.25mm) through US 15 (10mm) come with five needles per set.
The size is permanently laser imprinted on each needle.