When designing your hammock, rope swing, or bench swing, there are many materials decisions to make. There are the ropes, the seat, the mount point, the mount attachments, and potentially many other extras that can be involved.
With the seat material, especially for hammocks, the material choices vary: Cotton is regarded as the softest in feel of all. The nylon hammock is a bit sturdier and more durable in high humidity. Nylon, however, can be less successful in high sunlight environments. This is because today's nylon hammocks are actually polypropylene, which gets degraded by UV radiation. All hammocks can fade over time, particularly the darker colors.
If you don't have a safe place to hang your swing, have a look at the many styles of free-standing swings available to place on a deck or lawn. A 1 inch thick manila or sisal rope will be easy to hold on to and very safe. However, be aware that manila has a tendency to rot and over time could break, putting someone at risk. Choose sisal for longevity. Sisal or manila rope need some attention at the ends to prevent the fibers untwisting and coming apart: coat the ends with rubber or whipping to prevent this fraying. Sisal and manila do give a more traditional look than synthetic ropes. Priming the seats and then adding multiple coats of paint is also a good idea.
Consider using a cantilever beam fastened horizontally to your tree, rather than attaching your swing directly to the branches. A beam or pole mounted to your tree will give a more evenly balanced swing axis, but may be a challenge to stabilize as it is not as solidly in place as a tree branch itself.
Another design factor to consider is safety. Think about things that might slip - and look to secure them so they don't. An S-hook can have a rope slip out, for example when someone suddenly gets up off the seat. This can result in the swing or hammock, and anyone or anything on it, suddenly crashing to the ground. A locking carabiner works better here. If your hardware consists of S-hooks, it's advised to look into some basic locking carabiners. (Even a non-locking carabiner can be opened by a twisting rope). Another thing that can slip is the knot itself. Use a good knot on your mount points. And any tree strap used should be set up to resist vertical motion. Make sure your entire support design considers the maximum weight supported by the swing or hammock itself.
A basic option that will suit many needs is this complete set single-rope Wooden Tree Swing:
Classic Wooden Tree Swing
Rope recommendations: twisted rope is stronger than braided rope of the same size. This rope offered by Rope King
For a more adventurous look, when creating a swing with 2 ropes, you can also use mountaineer's climbing rope: Dynamic Rock Climbing Rope 
Materials tips:
Begin with enough rope that knots can be tied on both ends, and leave a little extra - cut off any excess rope so that the rope does not touch the ground.
For wood parts: sand all the edges, then prime with an outdoor wood
primer. Have your child decorate the swing with acrylic paints
(freehand or with stencils), then cover it with a coat of protective
clear varnish.
A do-it-yourself (DIY) swing can feature a cut board, a round circle, a tire, a belt, or a log for the seat. A nice Polymer Belt Seat
Construction will need to be sturdy - try the rope swing by standing on the knots and the seat. Kids will want to play with the rope swing in many different ways such as sitting on it, standing on it, in pairs, etc.
Materials Considerations
- Fade, mildew, and weather-resistant rope and fabrics
- Quality varnish on the wood
- Rust-proofing on the metal (galvanizing, zinc chromate are examples)
- Fade and mildew-resistant rope
- Strong overhead support
- free-standing swings are available for deck or garden landscape. An example is the
Free-standing A - Frame Yard Swing
which is a good size for 2 persons.
which is a good size for 2 persons.
Although only 12 inches, it's sturdy and comes in a variety of colors.
Some single-rope swings
only offer a 3/8th to 1/2 inch rope which may be made of nylon, plastic or
cotton -- not ideal since they stretch. Also, kids have difficulty holding the smaller ropes. 
by Furniture Creations.
, this complete set is made with durable plastic, steel and nylon rope materials, and holds up to 350 pounds of weight. (It also includes mounting hardware and illustrated assembly steps).
The Swing-N-Slide Tire Swing features a twisting, spinning design and includes 4 lengths of rope that attach to a 360 degree spinning swivel mount. It's extra sturdy with these 4 ropes for support, meeting national Safety Standards.
