You might find this useful...

http://www.sail-making.com/dbimgs/1%20All%20About%20Sailcloth%20End%20User.pdf - http://www.sail-making.com/dbimgs/1%20All%20About%20Sailclot h%20End%20User.pdf

There are others on there as well.

Harry

Aramid is the scientific name for Kevlar, Wombat is right.

It is used as the fibre matrix in laminate composite sails because it is light for its strength and does not stretch or creep. Unfortunately it is degraded massively by UV light and doesn't get on well with salt and abrasion. So it's important to encase it well and make it the middle part of the sandwich.

Dacron is another trade name for a polyester cloth that is the basis for most traditional boat sails (Laser, Topper, etc). It doesn't give the same strength to weight ratio as composite but it is cheaper and less fragile. For this reason, even on high perfromance boats, it is often used for jibs which will spend more of their lives flapping than a mainsail.

Kevlar ropes are a nightmare to work with as they are difficult to cut and kevlar doesn't melt so heat-sealing a line is difficult. Also, becasue they don't stretch or creep, you get no warning before they do fail. So don't use Aramid-cored ropes for climbing.

Most laminate sails use Mylar but I'm not sure about Kevlar sails as I've never owned one. Mylar is another trade name I'm afraid - the stuff is actually called biaxially oriented polyethelene terephthalate and it's used because it's tough and chemically very stable.  Get in touch with North Sails - they do a lot of the hi-tech stuff. Also I see that Y&Y have a feature on sail technology in the next issue. In the UK, Hyde sails are very approachable, give them a call.

The idea behind all composite materials is that the fibres of the reinforcement material, whether it be glass, carbon or kevlar are aligned to give they greatest tensile strength in the desired direction. The matrix is the "filler" and is there to keep the fibres in the right position and transfer the load if a single fibre breaks. In the case of sails, Kevlar is the reinforcement and Mylar the matrix. For GRP the glass fibres give the strength and the resin (epoxy or polyester) fills the gap.

Because woven materials have the weft and weave at right angles, sail makers can create strength in particular directions by stitching together panels in different orientations. North's 3D technology enables the whole sail to be laid up in one go so no panels are needed. In theory. However, this is expensive to make and one tear trashes the whole sail rather than a panel so those of us without Americas Cup budgets tend to go for a compromise.

Hope this helps. If there are any mistakes in the above I'm sure someone else will correct them.