A, B, C and E flute: what the letters mean

Every quote we send names a flute, usually with a letter. Most buyers do not ask about it, but the flute changes how a box behaves almost as much as the number of plies.

The flute is the wavy middle layer of corrugated board. Larger flutes are taller and wider waves; they give more cushioning and more stacking strength, but a rougher surface. Smaller flutes are thinner and flatter; they print better and fold more neatly, but cushion less.

A flute is the tallest, about 4.5 to 5 mm. It gives the most cushioning and is used for fragile goods. We use it less now, because C flute does most of the same work with less paper. C flute, about 3.5 to 4 mm, is the general-purpose choice and the one in most of our 3-ply shipping cartons. B flute, about 2.5 to 3 mm, is stiffer and resists crushing at the edges, so it suits heavy, compact products such as canned food, hardware and bottled goods.

E flute, about 1.2 to 1.6 mm, is the thin flute used in our mailer boxes. It takes good print, folds into crisp tuck-in lids and keeps an online parcel slim, though it is not meant for heavy loads. In 5-ply and 7-ply board, we often combine flutes, such as B and C, to get both crush resistance and stacking strength. Tell us what goes inside and how it travels, and we will suggest the flute.