Polypropylene gift-wrapping ribbon is very strong and colorful, but it is difficult to attach centerweighting in a really permanent way.

The best design so far is an unsymmetrical sandwich of 3M's #863 tape (a transparent monofilament-reinforced polypropylene strapping tape), which is very strong for its weight and lets the color of the bottom layer show through, with a narrow middle layer of polyethylene adhesive tape as the centerweighting, and a bottom layer of 50-micron (2-mil) thick colored polyethylene bag plastic from bearclaw.net.

There are apparently no retail sources for the 3M #863 tape---you have to order a carton of 36 from a tape wholesaler.

Centerweighting
To fly, a skybow needs a strip of stretchy material (centerweighting) running along the center of the ribbon. The centerweighting, needs to be stretchier than the rest of the ribbon so that it shares little of the ribbon's tension. Inelastic materials will not have a stabilizing effect.

Roughly speaking, the centerweighting should increase the weight of the ribbon by 50% and be narrower than 75% the ribbon width.

An adhesive vinyl tape, such as electrician's tape, can be simply stuck on one or both sides of a ribbon, or a non-adhesive vinyl tape, such as surveyor's flagging tape, can be used in a sandwich construction. Polyethylene adhesive tape, such as "Frost King Weatherseal Tape," which is used to install plastic-film storm windows, is better than vinyl because it is less prone to delaminate.

Other stabilization methods
It seems that the function of the centerweighting is to make tranverse waves move along the skybow more slowly than the torsional (twist) waves. There two other ways to accomplish this same end:

1) carry all the tension at the very edges of the ribbon by placing low-stretch fibers there, or

2) give the a ribbon a tube-like cross section so it can act a like a flexible shaft.

These should be fruitful areas for research.

Weight
Skybows rely on damping from aerodynamic forces to spin smoothly, so the skybow must be rather light. A rule of thumb is that the skybow should not weigh more than 15 times the weight of the air in the cylinder that circumscribes it. For example a 17mm wide skybow can spin smoothly if its weight is 4 g/m---and even lighter is better.

Stiffness
A skybow does need a certain stiffness across its width so that when twisted under tension it will not buckle and twist up like twine.

Swivels
The ends of a skybow segment must be held by very low friction swivels. Only high quality (e.g. SAMPO) ball-bearing fishing swivels will work. Use the largest size you can find, as the small ones will wear out in a few minutes even though the tension is moderate. For some reason the black swivels last longer than the nickel plated ones. Lubricate each swivel with a drop of sewing machine oil. Do everything you can to keep the swivels out of the dirt.

For long-life swivels you have to take the trouble to make your own, using quality ball bearings with rubber seals. I am using MR115-2RS bearings from bocabearings.com.

Length
A skybow needs to be long enough to power the spinning of its bearings. This minimum length depends on the width of the ribbon. We've had success with 30m lengths at 19mm width, and 50m lengths at 15mm width. When multiple segments are used in a bow (as in Mr. Big), the segments can be shorter since in general one segment only needs to power one swivel instead of two. Most recently I have been making 17mm-wide skybows with multiple segments just 24m long. In the eastern U.S. the flying fields are never big enough, so short segments are more convenient.

The longest single section we've flown was about 114m, but really long single sections are in danger of twisting up like twine if the windspeed varies greatly along the length of the bow.