ECT refers to the 'Edge Crush Test' that measures the strength of a piece of cardboard edge to edge (against the “grain” of the ridges, known as “flutes,” between the outer sheets) when compressed. This is an important indicator of how strong a box will be after its assembled, filled, and stacked. 32 ECT is the standard used for shipments between 25 and 44 lbs, under routine packing, shipping, and warehousing conditions.