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What is Air Dry?

Customers sometimes ask Canfor to explain how air dry weights are calculated. On this page we try to explain how the calculations are made, what the terms mean and we provide a link to an interactive model where you can explore the calculations yourself. First lets look at the terms:

GROSS WEIGHT - this is the weight of pulp as scaled at the baling line in the pulp mill, including wrap and wires.

SHIPPING WEIGHT (BILL OF LADING WEIGHT) - The agreed weight used for shipping by land or sea, this
weight is used by the carrier for billing the shipping mill. An allowance is made for weight loss due to
evaporation. Gross weight less 1% equals the shipping weight.

OVEN DRY (OD) OR BONE DRY (BD) WEIGHTS - Weight of pulp after all moisture has been evaporated.
This is calculated by oven drying of pulp samples at the mill until they reach constant mass.

AIR DRY - For pricing market pulp there is an internationally accepted convention that 1 Air Dry tonne of pulp contains exactly 900 kg of bone dry fibre and 100 kg of water, in other words it has a 10% moisture content.
The amount of moisture actually contained in 1 Air Dry Tonne will often differ from this 100kg, so the Air Dry mass that is billed has to be adjusted accordingly.

AIR DRY WEIGHT (ADMT = AIR DRY METRIC TONNE) - This unit of weight is used for pulp pricing. At the time of manufacture each bale has a somewhat different moisture content, usually not exactly 10%. So the weight of the bale is recalculated to allow for the difference in moisture between the nominal 10% and the actual level. This is the mass that is billed to the customer. Since Air Dry weight is a calculated value, it will only correspond with the actual weight of the bale if the bale moisture content was exactly 10%.

Generally, lower Air Dry of market pulp (86 - 90%) is easier to repulp at the point of consumption.

However, a lower percent Air Dry results in higher shipping weights, therefore incurring higher shipping costs.

ISO TESTING PROCEDURES - The internationally accepted procedures for conducting accurate moisture tests on pulp and pulp shipments are detailed in the following ISO Procedures, only parts 1 or 3 apply to Canfor pulps.

ISO 801-1:1994(E) Pulps - Determination of saleable mass in lots - Part 1: pulp baled in sheet form
ISO 801-2:1994(E) Pulps - Determination of saleable mass in lots - Part 2: pulps baled in slabs
ISO 801-3:1994(E) Pulps - Determination of saleable mass in lots - Part 3: unitized bales

available from ISO Secretariat

Click here to run our Air Dry statistics calculation model.