1. E flute features a small flute profile, providing great printability and a smooth surface finish.
2. C flute features a intermediate flute profile, providing a balance of stackability and cushioning.
3. F flute features the finest groove profile. It's commonly used in cosmetic packaging.
4."A, B, C, K" refers to the flute profiles categorized by their groove. The general rule is that the earlier in the alphabetical order, the stronger the flutes are.
5. The "+" sign refers to the increased thickness of flute for higher stiffness and hardness.