Understanding Line Stretch: Why It Matters and How to Measure it.

The stretchability (or elongation) of a fishing line is expressed as a percentage. In everyday life, we use different tools to measure various things: a tape measure for metres, a ruler for centimetres, or a micrometer for highly precise measurements in millimetres or microns. However, there’s no dedicated instrument for measuring line stretch—because stretch doesn’t exist independently. It only occurs when force is applied.
This is a critical concept to grasp. For example, a 0.50 mm line and a 0.20 mm line will not stretch the same way under identical tension (e.g., 2 kg), even if both are labelled as having a 15% stretch rate. That’s why understanding line stretch is essential when choosing the right line for your carp fishing style.
How Stretch Affects PerformanceBefore we get into how to measure line stretch—particularly in monofilament lines—let’s first explore what stretch actually impacts.

Monofilament Line Categories by Stretch:

• Very Low Stretch – up to 10%
• Low Stretch – 10% to 15%
• Medium Stretch – 15% to 20%
• High Stretch – above 20%

Stretch influences both casting performance and bite sensitivity. Selecting the right stretch level depends on your fishing scenario. Choosing the Right Stretch for Different Scenarios:

Scenario 1: Long-Distance Casting
To achieve maximum casting range, you typically want a line with:

• Minimal diameter
• High smoothness
• Softness and low weight

However, ultra-thin and lightweight lines often have lower density and higher elongation, which can reduce bite detection and responsiveness.

Scenario 2: Precision Casting with a Line Clip
When casting to a clipped distance, accuracy is critical. In this case, a low-stretch line is ideal. But these lines often come with trade-offs:

• Increased stiffness
• Higher density
• Reduced aerodynamics

So, there's always a balance between stretch, casting distance, and sensitivity.
Finding the Right BalanceChoosing the correct line diameter and stretch level should depend on the specific fishing situation.
For example: If you’re fishing within 100 m, there’s no need to use ultra-thin, high-stretch lines. A 0.30 mm or even 0.33 mm line will give you better control and higher casting accuracy.

Key Principles to Remember:

• No force = no stretch
• Under the same force, thinner lines stretch more than thicker lines
• Most manufacturers do not specify the conditions under which their stretch percentages are measured—test it yourself when in doubt

Common mistake: measuring stretch to the Breaking Point. A frequent mistake is testing line stretch up to its breaking point. However, this isn’t practical—because in real fishing situations, you should never apply that much force.

Example:
During a fight with a carp, it’s recommended not to exceed 50% of your line’s actual breaking strain, especially if you're using weaker knots.
Curious about how much the line stretches when a spomb or spod rocket hits the clip at 100 m? It depends on many variables: rocket weight, casting force, and the angle at impact — too many factors to calculate precisely.

How Katran Measures Line Stretch

At Katran, we test stretch under real-life conditions. Here's how we do it:

• We apply 50% of the line’s actual breaking strength to a 1 m sample
• The amount it stretches in centimetres is recorded
• That value is then converted into a percentage—this gives you the true stretch rate