The resulting chair is really comfortable. It feels like sitting on rubber bands. The trick is to have narrow enough spacing and a tight-enough weave so that your weight is evenly distributing across as many lengths of hose as possible, which will in turn evenly distribute the stress on the hose, preventing sagging and long-term decay.
The overall form is quite reclined, with an interior width of about 22". Assuming the hose is recycled (garden hose would work as well, though it typically is made from thinner rubber), the only other materials are one 2'x 2' piece of 3/4" plywood and four 2' x 1/2" dia. threaded rods with nuts and washers. There is almost no waste from the process, making it quite efficient for both the environment and your wallet. Out-of-pocket costs are about fifteen-twenty bucks, depending.
Step 1: Framin'
Lay out your pieces, and cut with a circular saw, jigsaw, or bandsaw. Cut the leftover center piece into four roughly equal pieces, or two pairs of matching pieces. I made the back legs a little wider than the front.
Lay the legs on top of the "Ls" and play around with them until you have both an angle of recline that you feel comfortable with as well as a decent height off the ground. My version is only about a foot from the ground to the seating surface at its lowest point. Run a straightedge over the feet to derive the angle at which they will meet the ground and cut off.
Glue and screw the legs to the inside of the "Ls."
Step 2: Holes
Lay out four holes for the threaded rods as well; one at each end of the "L", one at the crook of the "L", and one connecting the back legs near the bottom. Countersink the washers and nuts for a finished appearance. Try to keep the rods as far from the seating surface as possible so they do not interfere with the hose as it sags.
Step 3: Finishing
To clean up the edges, even out the appearance of straightness, and make the chair smoother to the touch, run a roundover bit in a router all the way around each piece, then sand thoroughly, first with 100 grit, then 120. You could also use a chamfer; I would just recommend that any edge treatment be on the heavier side, say 1/4"-1/2", to make the chair inviting to the touch.
Assemble with the threaded rods. use a ratchet and wrench to tighten the threaded rods and rigidify the chair.
Apply 2-3 coats of polyurethane or similar with a soft rag. Sand with 220 or 320 grit between coats. Do not worry about getting in all the hose holes, as they will be hidden from view. Once the finish is dry and hard, buff in a coat of furniture wax for maximum smoothness.
The last picture shows the total waste from the project; eight small scraps of wood and a small pile of sawdust.
Step 4: Hosin'
At each hole, brace your feet against the frame and pull the hose through with both arms as hard as you can, to stretch the hose tight. Being rubber, it will inevitably sag over time, so it's best to get it as tight as possible now.
These hoses can handle a tremendous amount of force. Not shown here is my first attempt at this chair, using reclaimed pallet wood. I stretched the hose so tight it snapped part of the frame off, which flew up and almost busted me in the jaw. The plywood in this version is a much stronger material.
That said, you can see in the first photographs in the introduction that sides of the frame curve inward and the legs belly out from the tension of the hose. The threaded rods are also bent into slight "smiles" from the same force; this isn't such a bad thing, as it bends away from the surface of the seat, accommodating the sag of the hose when someone is sitting there.
Sit down and enjoy!