You will need the following:
Tack hammer & tacks, or staple gun
Webbing
Webbing stretcher
Stanley knife or strong scissors.
You can buy webbing and the stretcher at your local craft shop.
If you can't access the existing webbing from the top of the chair you may have to turn it upside down and remove the fabric panel.
Note how the existing webbing is attached and interweaved before you remove it. Draw a sketch or take a picture.
Don't cut any webbing just yet!
Remove the old webbing and tacks/staples.
Fix the webbing at one end, then thread the first strip.
To make the webbing taut you'll need to use the stretcher. Thread a loop of webbing through the slot in the stretcher and insert the friction pin. Then use the stretcher to get leverage against the chair frame to reach the required tautness.
It might help to have another person work the hammer to affix the second end while you stretch.
Cut the webbing to length after you have fixed it in place.
Lay all the strips of one direction of webbing first, either way it doesn't matter.
Then weave the cross direction, over & under.
Big Softy, February 2007