Plastic bags make good cordage for the same reason they make good rain gear: the film is thin, but it is tough, it does not rot, and it stretches before it tears. Twisted into a two-ply cord using the reverse wrap, the same technique used for plant-fiber cordage, a single bag produces several feet of line that is strong enough for camp work.
You will need
- One or more plastic trash bags. Thick contractor bags, 3 mil or heavier, make much stronger cord than thin kitchen bags.
- A knife or scissors
Preparing the strips
- Lay the bag flat and cut off the bottom seam and the drawstring hem at the top. What remains is a flattened tube.
- Cut across the tube to make loops about 2 to 3 inches wide. Wider loops give thicker, stronger cord.
- Cut each loop open to make a long flat strip, or keep them as loops and chain them together by passing one through the next and pulling tight.
For one continuous strip instead, cut the flattened tube in a spiral, working around and around from one end to the other.
Making the cord
- Take a long strip and fold it at a point about a third of the way along, not in the middle. The two legs will be of unequal length, which means the joins added later do not all fall in the same spot.
- Pinch the fold between the thumb and forefinger of one hand.
- With the other hand, twist the leg farthest from the body tightly away from the body, then bring it over the near leg toward the body. The legs have now changed places.
- Twist the new far leg away, and cross it back over toward the body.
- Keep repeating: twist away, cross over, move the pinch point along. The plastic rolls into a tight rope as it goes, and the opposing twists lock each other in place so the cord does not unwind.
- When one leg runs short, lay a new strip alongside it with a few inches of overlap and twist both together as one.
To finish, tie an overhand knot in the end. Rolling the finished cord firmly between the palms tightens the lay. For a heavier rope, reverse-wrap two finished cords together, or braid three of them.
What it is good for
Trash bag cord handles light and moderate loads: lashing poles for a shelter frame, running a ridgeline for a tarp, a clothesline, tying bundles of firewood or gear, or replacing a broken strap. It holds knots well and does not absorb water.
It has limits. Plastic creeps under a steady load, sunlight makes it brittle within weeks or months, and a nick at one point weakens the whole line. Never use improvised cordage of any kind for climbing, lowering a person, rescue or anything where a failure could injure someone. Check it before each use and replace it once it turns chalky or starts to split.
The same method works with plastic grocery bags, woven feed sacks and many plant fibers.