A Flute - 5mm - Good stacking protection.
B Flute - 3mm - Good puncture resistance.
B Flute - 3mm - Most common grade.
E Flute - 1.5mm - - Lightweight fine flute.
AB Flute - MFlute double wall 7mm - combination of A + B Flute.
BE Flute - Flute double wall 3.5mm - combination of B + E Flute.