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
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
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
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
Bone Dry weight = Air Dry weight * 0.9
Air Dry percentage = (Air Dry weight * 100)
/ Gross weight
Air Dry weight = (Gross weight * Air Dry percentage)
Click here to run our Air
Dry statistics calculation model.