Why Grain Direction is Important

Gane Brothers & Lane, grain direction

When paper or board is manufactured, the fibers from the
pulp line up in the direction that the machine travels. This is called grain
direction or machine direction.

Usually a sheet is designated “grain long” or “grain short”.  Frequently the second dimension will tell you
the grain direction, i.e. 8 x 10 would have the grain direction in the 10”
direction, or grain long.  You can’t
always depend on the second dimension being the grain direction, so you need to
make sure.

Why it is important:

Folding – It is important to fold in the grain
direction.  Folding cross-grain will
break more fibers, thus giving a more ragged and weaker joint.

For book covers and boxes, it is important to have the fold
in the grain direction to avoid product failure. 

Binding – Grain direction of pages should run parallel with
the spine because of absorption rate of moisture.  Cross grain absorbs 4 times as much moisture
as grain direction.  Spine of book could
become warped if page grain direction is wrong.

Machine direction is also important for PVC.  It is vital that all pieces of vinyl that
will be heat-sealed are laid out in the same direction.  PVC may stretch when being rolled off, and
sealing material with a different machine direction will most likely cause
wrinkling.

How to determine grain direction:

In paper: fold and see which gives a cleaner edge.  Folding with the grain gives a cleaner edge.
Or you can apply moisture to one side and watch which way the sheet curls.  Grain direction is the direction of the curl.
Also try tearing a sheet of paper to indicate grain direction.  Tearing with the grain will result in a
straighter, less ragged tear than tearing against the grain.

For board and thicker material: bend the sheet to see which
direction flexes more easily.  The
cross-grain direction will feel stiffer.