There are many brands, types and sources of fabrics for the modern kite builder. The most popular types are woven Ripstop Nylon Fabric (RSN) and Ripstop Polyester Fabric (RSP), These come in many weights and from several manufactures.
Most of these fabrics have a coating applied to reduce their hygroscopic properties and to reduce porosity. These coatings also stiffen the hand of the fabric, making it easier to sew accurately.
Every fabric has a use. There are pros and cons to every decision when we build kites.
Now to focus on Nylon
Pro or Con, Stretch. If you fly in gusty conditions this is the fabric of choice. The sail will give when a gust hits is and recover its shape. Nylon fibers have up to 50% stretch, more when wet or damp from a high humidity day. But if you are looking for the top performing fabric than the stretch most likely be a liability.
Pro, Cost. Nylon is usually the least expensive of all the usual kite fabrics.
Pro or Con, Weight. Nylon is usually available in 1.5 and 0.75 oz per sailmakers yard. This weight is taken BEFORE the coating goes on for most fabrics, so your fabric may be marketed as 0.75 oz, but some have weighed some in at 1.7 oz per yard. Challenge is making a true 0.4oz Nylon but has limited availability and is about $10/Yd at Kite Studio and only comes in white, but you can dye it at home. Kite Squid’s Iris Blossom Edo kite that is in the photo album was made from it. He dyed all the fabric himself! He has also had sucess dying Polyester fabric at home too. If you dye at home make sure you read and understand the MSDS for all the chemicals you are planning on using!!!!!!
Con, Water. Water bonds to Nylon, like a tick on a hounddog… You just can’t keep it off. Nylon is Hydrotropic meaning that water is attracted to the fibers. The manufactures coat nylon sail cloth with Silicones, Urethanes and other proprietary compounds in an effort to control the bias stretch of the fabric and to a greater extent, fend off water. A boat sail LARGE compared to most kite sails and they can get VERY HEAVY and stretched way out of shape when the get wet. Sailcloth absorbs water from the air on a humid day, or durring a light rain or fog, and when Nylon is wet it has more stretch than when it is dry.
Some comparisons between manufactures of Ripstop Nylon.
They are all Nylon woven in a Ripstop pattern.
Most RSN sold in to the kitebuilidng market is Type 6.6. Some overseas kite manufactures use type 6 Nylon to make thier kites.
The fabrics in one class are all about the same weight per area.
The differences are in the fine tuning the manufactures do in the weaving process and the coating process in an effort to make their product the best for a particular boat sail application.
MOST ripstops are warp oriented, meaning that the fibers that run the length of the fabric (the warp fibers or if you live in Great Brittan the woof fibers) are straightest and the weft fibers (the ones that go across the fabric) have more bends in them to make the weave.
The fibers with more bends in them straighten out under load and stretch a little more than the already straight fibers.
What does that mean to you? Cut the fabrics out so that the least amount of stretch is in the direction where you have the highest loads or where the shape in flight is more critical… something for you to decide or it might be in the plans.
Now we have to address bias stretch. The bias of a fabric is at 45 degrees to the warp and weft fibers. This is the line that the fabric will stretch most. To control this, the manufactures do several treatments to the fabric.
They can Calanderize (SP?) it. Meaning they mash the fabric between some heated rollers to lock the fibers together.
The can apply a proprietary coating to the fabric in an attempt to bond the fibers together. The coating also usually provides some UV protection and they also try to keep water from bonding to the nylon fibers.
What does this all mean to you?
You should buy the ¾ Oz nylon in the colors you like but try to build one kite with fabric from one manufacturer. You don’t have to stay to that guideline, but do NOT mix types of fabrics in one kite i.e. mixing Nylon and Polyester in the same kite as they have different amounts of stretch.