Definition
In a woven fabric, the threads that run crosswise — perpendicular to the long edge (selvage) of the cloth. They interlace with the lengthwise warp threads to form the weave. Also spelled 'weft.' In aircraft fabric covering, the woof threads run across the width of the bolt of fabric.
Plain English
The threads in a woven cloth that go side-to-side across the fabric, weaving in and out of the threads that run the long way.
Context Anchor
Seen in aircraft fabric covering, fabric repair, and fabric inspection discussions.
Derivation
From Old English 'wefan,' meaning 'to weave.' 'Woof' is an older form of 'weft.' Both refer to the threads carried back and forth across the loom by the shuttle, perpendicular to the fixed lengthwise threads. Knowing this helps because the term has nothing to do with sound or with a dog — it's purely a weaving word.
Why Pilots Care
Aircraft fabric has different strength and stretch characteristics along the warp versus the woof direction. Mechanics covering or repairing fabric surfaces must orient the cloth correctly so loads are carried by the intended threads, and so shrinkage and tension behave as designed.
Analogy
Think of a piece of woven cloth like a grid. The woof threads are the lines running side to side across the grid.
Intuition Check
“Woof” does not mean a dog sound here. In aircraft fabric work, it means the crosswise threads in woven cloth.
Example Sentence 1
When laying out the fabric on the wing, the technician aligned the warp threads spanwise so the woof threads ran chordwise across the rib.
Example Sentence 2
Damage along the woof threads required a patch that matched the original weave direction.