“Now over time, the finish will wear off on the lines, especially at points where they rub, it degrades in UV light, it gets rubbed off on sand on the beach. So, as this coating is breaking down on the outside of the lines, that hollow space on the inside of the line is open for tiny sand particles, salt, for things to get inside there. And if anything gets inside the weave of the line, the line will grow in diameter. Now, to grow in diameter, the only thing it can do is shorten in length.”
— Dave Kay
The Eternal Question: Do Kite Lines Stretch or Shrink?
One of the eternal questions in kitesurfing is whether flying lines stretch or shrink. Because lines are constantly pulled by the powerful force of the kite, it feels natural to assume they stretch like rubber or standard rope. However, based on physical mechanics, the most prominent change that occurs in kite lines is actually shrinkage.
Kite lines are made of ultra-high-molecular-weight polyethylene (UHMWPE), most famously known under the brand name Dyneema. During manufacturing, the polyethylene molecules—which naturally resemble a tangled bowl of spaghetti—are stretched out into extreme linear alignment. Because the polymer retains a memory of its original state, the molecules naturally attempt to tangle back up over time, meaning even a bare fiber sitting on a shelf will slightly shorten.
An even greater factor is the intrusion of foreign contamination described by Dave Kay in the quote above. Once the outer coating wears down, sand particles and salt crystals penetrate the hollow space inside the 12-strand braid, increasing the line’s diameter and forcing its overall length to shorten.
During riding, the front lines constantly bear roughly ten times the load of the rear lines. While this heavy load resists shrinkage on the front lines, the lightly loaded rear lines shrink much faster. When riders using a worn control bar feel as though their front lines have stretched, it is actually an illusion caused by the rear lines shrinking and becoming relatively shorter.
How to Adjust Shrunken Lines (Line Stretching) and Its Caveats
As explained above, lines shrink far more often than they stretch. Particularly when the rear lines shrink and no longer match the length of the front lines, a common field adjustment is to physically pull the shorter lines under heavy load to stretch them back out.
By securing the lines and pulling hard to load them back up, riders can straighten the fibers and tighten the weave to even out the lengths. However, as Kilian from the specialist line brand The Line Smith points out, stretching lines back to normal only holds for about 20 minutes to an hour before they shrink right back to where they were before. Therefore, to permanently resolve uneven line lengths, it is necessary to adjust the knot positions on the control bar or add pigtails to restore proper trim.
The Line Lifecycle: From the Honeymoon Phase to Replacement
From the moment a brand-new set of lines is unrolled until it reaches the end of its lifespan, the condition of the lines progresses through three main phases.
1. The Honeymoon Phase (Initial Settling Time)
Inside the braid of brand-new lines, manufacturers must leave a small amount of air; without it, splicing the loops at the ends of the line would be nearly impossible. When heavy loads are applied during the first few sessions (roughly the first 4 to 5 days or 20 hours of riding), this air is pushed out of the 20-meter length and the braid settles, increasing the front line length by around 3 to 5 centimeters. Because the rear lines simultaneously begin their initial shrinkage, it is essential to check line lengths and re-tune the bar within the first week or 20 hours of use.
2. Mid-Life Wear
As sessions accumulate and the surface coating slowly wears off, salt crystals and sand penetrate the braid, triggering ongoing shrinkage. Daily maintenance during this phase dictates how long the lines will maintain their trim. Simply rinsing the bar and lines in clean fresh water after every session prevents salt crystals from building up inside the weave, significantly slowing down shrinkage. Checking and adjusting line lengths at least once a month over a season is a reliable rule of thumb.
3. Time for Replacement
The lifespan of a set of lines is measured not in time, but in cycles—specifically, how many times the lines rub against each other under tension. While a rider who never crosses their lines might use the same set for six or seven years, riders who frequently throw kiteloops and sheet the bar up and down over the 50 to 80 centimeter depower throw with crossed lines subject the lower 4 to 5 meters of their front lines to intense abrasion. Applying line wax to lubricate the lower front lines helps prevent friction and heat buildup, but once you can feel rough spots or fraying when running your fingers along the lines, or when length discrepancies exceed adjustment ranges, it is time to replace them.
The Evolution from Dyneema to SK99 and SK99+
Dyneema is simply the protected brand name for UHMWPE fibers produced in Holland; Dyneema itself only manufactures the raw fiber, not finished kite lines. Designations like SK76, SK78, and SK99 are internal codes for the grade of that base fiber. As the newest grade, SK99 is roughly 30% stronger than SK76, allowing for thinner lines with less drag. However, because individual SK99 fibers are thinner, they offer slightly less abrasion resistance than the thicker fibers of SK76, presenting a trade-off between pure performance and multi-year longevity—especially on low-V bars where lines rub more than on high-V bars.
In recent years, SK99+ (Plus)—which has become highly sought after among professional riders—differs fundamentally in its coating process. With standard SK99, 12 strands are braided together into a line first and then passed through a coating bath, leaving the coating only on the exterior of the line.
With SK99+, the coating process is moved to the very beginning: each thin, hair-like yarn is coated individually before the line is braided. Because every yarn is protected on the inside as well as the outside, dirt and salt cannot penetrate the core even after the outer coating wears away. This provides strength from the inside out and dramatically improves length stability.
Bridle Line Stretch and Shrinkage
Because the bridle lines on the kite itself are made from the same braided materials, they experience a small elongation of around 2% to 5% under load. However, because bridle lines are quite short compared to flying lines, the actual change in length is so minuscule that riders will not feel it during normal sessions.
That said, if a kite goes into a death loop or a line snaps, an extreme asymmetrical load is punched into one side of the bridle. Because the line elongates under that massive shock load and then shrinks back further over a few hours than the side that did not take the punch, repeated heavy crashes can eventually cause a slight imbalance in the bridle trim.