You can build a tree swing in a number of different configurations: a double or single rope, a tire swing, or even a chair swing. The type of tree swing determines the kind of rope that will best support and distribute the weight of the person and the swing.
Twisted and braided are two types of ropes. Individual yarns are twisted together to form strands that, in turn, are twisted together to form a spiral that becomes the rope. Braided rope consists of individual strands that are interspersed by weaving over and under the same as you would braid hair. Different materials and patterns create variations of twisted and braided ropes with some more sturdy than others. Twisted ropes are easier to splice to create longer pieces but this shouldn't be an issue with making a rope swing. Choose the rope based on strength and size rather than type.
Common rope fibers consist of natural manila, polyester, nylon and polypropylene. Polypropylene is a property of the Poly-Supreme rope recommended by Wood Tree Swings as the best rope for tree swings. It is strong, lightweight, waterproof and holds a knot well. Mother Earth News advises against nylon rope as being too slippery and natural manila because it will eventually rot. Mother Earth News recommends a poly-twist type rope.
Sizes and Lengths
To figure the length of rope needed for a double rope tree swing, multiply the height of the swing from the ground by two plus an additional 4 yards. For a single rope swing, cut the final number in half. The extra 4 yards allows for the overhang on the tree and underneath the seat of the swing. Use a rope with a diameter of either 3/8 or 5/8 inch.
Inspect the swing yearly for wear and tear and replace parts as it becomes necessary. Good quality ropes should last for over five years according to Tree Top Builders. Go through swing safety procedures with your children and make sure they hang onto the ropes with both hands at all times.