Humidity and the Classical Guitar

by Dave Belcher

Here in the Northern Hemisphere we are approaching the season of Winter. Winter is not a great time of year for our instruments. The colder air in many places, along with the use of heating in our homes, causes the air to dry out. The drier air can damage guitars in a number of ways, some of which can be pretty catastrophic.

So in this article we’ll be looking at ways to humidify your instrument, danger signs to look out for, and recommendations for equipment.

But before we get started, we want to share with you a video from New Jersey luthier and good friend of CGC, Gary Lee. This video comes from Gary’s Masterclass on guitar mechanics at CGC Academy. (Many thanks to Gary for allowing us to use his video and for providing advice and funny stories!)

An introduction to humidity and the classical guitar

First of all, let’s discuss relative humidity. Relative humidity (or “RH”) is the percentage amount of water vapor in the air relative to the temperature. As Gary says in the above video, we want our guitars to be in the general relative humidity range of the environment in which the guitar was built. That is typically somewhere between 40 and 50% RH. You may want to check with your luthier or do some research on where the guitar was manufactured to have a better idea of your guitar’s ideal comfortable humidity level.

Now it’s just a matter of ensuring your guitar stays somewhere around that RH level, especially during the winter months when it’s drier. (We’ll address high humidity briefly later.) So what are some good options to keep your instrument at its preferred RH level?

Classical Guitar Humidifiers

Internal Humidifaction System

Some people are lucky enough to have humidity control systems built in to their HVAC, or Aircon units. If this is you: congratulations, you have the best of all possibilities! Seriously, though: if you’re a guitarist, don’t update your HVAC system without asking for a humidity control attachment. Most modern-day HVAC systems already have some built-in humidity control. But you can also purchase separate attachments that can help you maintain a desired RH level.

Room Humidifier

Another solution is to use a large room humidifier. These should not be confused with the misting humidifiers from companies such as Vicks, intended to free up nasal passages. Instead, these are large units that hold gallons of water. They are meant to fill a large room or even an entire house. Typically, these large humidifiers have a filter that needs to be replaced every so often. They are often quite loud because they usually need to run the fan on the highest setting. But, they can easily battle the dry air and get you to a safe relative humidity. While both this and the first solution do allow you to leave your guitar out of its case, you will use a lot of water and the noise may be less than desirable. All of the following options, however, require you to enclose the guitar in its case (and in a good case!) when you’re not using it.

In-body Humidifier

Most guitarists today use a simple in-body humidifier. These much smaller humidifiers insert into the soundhole of the guitar and suspend between the strings. This style of humidifier usually features a sponge that you have to moisten once it dries. The humidifier takes care of the rest. An even better solution is the Oasis humidifier that uses a gel inside a water-sealed tube that you fill with a small amount of water. The downside of these humidifiers is you have to be careful to refill them with water often — and that requires a great deal of maintenance.

Case Humidifier

You can also place a humidifier inside your case. In fact, there is a case manufacturer called “Humicase” that has a built-in humidification system. And this brings up an important point. You really want to make sure you have a guitar case that provides an air-tight seal when it is shut. This means you should avoid cases that do not have a rubber seal along the lip where the case closes. The rubber seal keeps much needed humidity in, but also keeps out the dry air of the environment outside the case. So do yourself a favor and invest in a good case with a rubber seal! Some recommendations would be BAM, Visesnut, or other higher-end cases.

DIY Humidifier

But what about making your own? A simple solution many guitarists use is to take a sponge, moisten it in distilled water, and then place it in an airtight bag, like a Ziplock bag. Puncture the bag several times with a safety needle and place the baggie in your case. Homemade humidity! This has the same downsides of the in-body humidifiers in that you have to remember to make sure the sponge is moist, which requires regular attention and maintenance.

Two-Way Humidification System

The final and arguably best solution is D’Addario’s two-way humidification system. This system includes enclosed packs of gel material that you place in either the soundhole (suspended between strings) or under the headstock of the guitar, or both. What is great about the D’Addario system is that it does all of the work for you with no maintenance required. In fact, while they eventually dry out (after a long period of time) and require you to purchase new packs, there are even solutions that allow you to keep reusing the packs over and over. Once again, Gary Lee shared his wisdom with us at CGC’s Guitoberfest in 2020 on how to do that:

Danger Signs of Low Humidity

There are many signs that your instrument could be suffering from low humidity. We need to be aware of these signs so we can act fast to prevent further damage if they occur. But avoid all of these danger signs by keeping your guitar in its preferred RH level consistently!

The Frets

Stop me if this is you: After your last practice you left your guitar out on the guitar stand all night. It gets very cold this time of year and your house is drafty. You pick up the guitar the next day and the frets feel so sharp you feel like they’re cutting your hand. How did my frets grow?!

This is the most common sign of low humidity levels. Typically guitarists will describe this as frets that are “sticking out.” But that’s not the whole story. The frets feel like they’re sticking out only because the fingerboard has actually shrunk! When the fingerboard dries out too much, the wood contracts. And the bad news is, this is irreversible — you can’t put that wood back once it shrinks. However, your luthier can shave off the ends of the frets to make them even with the fingerboard again.

The Bridge

Another less common danger sign of low humidity on your classical guitar is the bridge beginning to pull from the top. A luthier who repaired one of my guitars decades ago gave the following advice. If you can fit a piece of paper between the bridge and the top, the bridge needs to be removed and reglued. Other repairs may be needed. Obviously were this to worsen the bridge could pull up off of the top and cause even more damage. Not. Good.


Finally, a very dry instrument can start to exhibit cracks — usually in-line with the grain of the wood. These can take place all around the instrument: on the top, sides, or back, and even at joints. These often require a repair that can sometimes be quite costly. You don’t want cracks in the wood of your guitar!

What about High Humidity?

Most of our guitars are not built in rain forests or tropical environments — even most luthiers that live in tropical environments in fact use humidity controlled rooms to build their instruments, and most keep the humidity between 40 and 50% RH. However, in an effort to make sure their instrument has a high enough humidity level, some guitarists will overhumidify. And while it is much less common than low humidity, high humidity is also not good for your instrument.

When there is too much moisture in your instrument, the wood expands, and this can loosen the glue at joints (including the glue of the bridge!), which can lead to some very bad things indeed. A great danger sign to look out for of humidity levels that are too high is the appearance of rust on your frets.


We hope this article has been helpful for you and answers some of your questions about humidity and the classical guitar. This is a very important area of guitar maintenance you don’t want to skip.

Many thanks once again to Gary Lee for his generosity and for sharing his wisdom and expertise with us.

The videos in this post come from CGC Academy, our online school for classical guitar. If you’d like to learn more and become a member today, find out how to join here.