Ask the Expert: What’s the Deal with Nylon Strings?

Guitar repair expert Martin Keith explains the differences between steel and nylon guitar strings and shares some useful terminology.
collage showing three different packages of nylon guitar strings

If you’re wondering about the differences between nylon-string and steel-string guitars, you’re not alone. Here we take a look at the strings that distinguish each of these guitars as their own unique instrument.

Q: I’ve been a steel-string player for years, but just got my first nylon-string guitar. I want to figure out what strings will work best for me, but the names and tensions are confusing. Can you help clarify things? —Rebecca P., via email

A: Thanks for the question! Rest assured—you are not alone. Players who come from the steel-string world are accustomed to the relatively simple system of numbered gauges (12s, 13s, etc.) standard among manufacturers. By comparison, the naming convention for nylon-string sets is a bit more poetic, and not quite as easily portable from one brand to another. The weights of string sets are usually indicated with terms such as medium hard, hard, and extra hard. To add to the confusion, many of these sets overlap in unpredictable ways—for example, La Bella’s upscale Argento line includes the same second- and third-string gauges in all three available weights.

Nylon-string sets also have wider variation in materials than steel strings, in all three main areas of construction: the core, the wrap, and the plain string. Let’s take a quick look at the differences available for each, along with some useful terminology.


Unlike steel strings, nylon sets usually have three wound strings (known as basses) and three plain strings (called trebles). The basses are wound with a metal wrap wire over a stranded filament core, made from either nylon or a blend of other synthetic fibers (such as in D’Addario’s Pro-Arté Dynacore line). The alloys used for the wraps vary and can have a big impact on the tone and response of the string. String manufacturers use wrap alloys ranging from traditional 80/20 bronze to more exotic choices, even pure silver in the case of La Bella’s Argentos.

At the dawn of the modern era of guitar, the only choice for treble strings was gut, usually sheep intestine. As an organic material, gut presents some difficulties—it will react to heat and humidity, causing tuning instability. During World War II, the supply of natural gut was restricted, as it was also the preferred material for medical sutures. In response to this shortage, the Augustine string company, in collaboration with E. & O. Mari/La Bella and with input from classical guitar legend Andrés Segovia, developed nylon trebles and formally introduced them to the market in 1948. Other makers soon followed, and the stability and predictability of nylon soon made it the material of choice.

Because of the inherent properties of nylon—and the processes used in its manufacture—the shape and diameter of clear nylon strings is not always perfect. There can be tiny variations along the length of a string, which are too small to notice, but just enough to affect the string response, particularly the intonation. To address this, string makers developed rectified strings, which begin as clear nylon and are then ground to precise shapes and sizes. The resulting strings hold closer tolerances for dimensions along their length, which improves intonation and consistency. However, the grinding process leaves a textured surface on the string, quite different in feel from the slick, smooth feeling of clear nylon. Some players experience more string squeak and noise with rectified strings. They are also generally felt to be a bit warmer-sounding than clear nylon trebles.

Black nylon trebles are most often seen on older folk nylon guitars and are typically associated with a softer, warmer tone and less clarity and articulation. The lower tension of these strings is also a good fit for beginning players or those with less hand strength. These strings are usually equipped with ball ends, which simplify stringing vs. the traditional knot-style bridge attachment.


In recent years, carbon and other composites have entered the market. Carbon compositions are denser, and therefore a thin carbon string will have equivalent mass to a thicker nylon string. Carbon trebles are usually thinner than nylons, and offer a brighter tone with more overtone content—both of which may make them a more familiar-feeling choice for a steel-string player looking to cross over.

Classical guitar technique places considerable emphasis on clarity, note separation, and independence of voices within a given chord shape. Many classical guitarists also prefer notes with a strong, impulsive attack and relatively modest sustain. Good classical guitars—and their strings—have evolved to emphasize these traits, but those same characteristics may not be ideal for other genres, such as bossa nova, jazz, or even modern fingerstyle. Furthermore, crossover steel-string players may not have the well-groomed and sculpted fingernails of a serious classical player, and may prefer to play with the fingertips themselves. In cases like this, the modern, brighter strings may help to keep things sounding crisp without the help of a fingernail attack.

Alongside your playing style, your instrument itself can inform your choice of strings. Cedar- or redwood-topped instruments are generally warmer and darker sounding than those with spruce soundboards, and your choice of string can either balance that or further emphasize it, depending on your preferred result.

Much like violinists, classical guitarists converse at great length about the minute differences between string brands. Unlike electric players (or even many steel-string acoustic players), classical guitarists have relatively fewer key variables that determine their sound: the guitar itself, their own technique, and their choice of strings. As a result, there is a wealth of information online about the tonal characteristics of the different brands—though, as always, one should take online advice with a healthy dose of caution.

Strings are a relatively inexpensive way to fine-tune the feel and tone of your guitar to suit your specific needs. And with nylon-string guitars particularly, the broad range of options gives the player quite a bit of control. Although different strings will not completely change the inherent character of a guitar, the right choice can emphasize the best aspects of your instrument and style, and make playing more comfortable and more fun.

Martin Keith is a luthier, repair and restoration expert, and working musician based in Woodstock, New York.

AG 320 JAN/FEB 2020 - Molly Tuttle

This article originally appeared in the January/February 2020 issue of Acoustic Guitar magazine.

Martin Keith
Martin Keith

Martin Keith is a luthier, repair and restoration expert, and working musician based in Woodstock, New York.

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  1. Hello,
    I have a Baritone Ukulele. I would like to be able to replace the nylon D string (only) with a metal D string so I could trigger an electric guitar (magnetic) pickup.
    – I want to do this so I can isolate the D string and send it through an Octave pedal for a bass guitar sound. Of course the internal microphone would still pick up all the strings as usual.
    I realize that instruments designed for nylon strings typically are not able to withstand the tension of metal strings.
    My question is…
    Have there been any developments with metal strings that have reduced their tension to close to that of nylon strings…maybe to improve flexibility?