The ideal humidity range for acoustic guitars is between 45 – 55%. Use a hygrometer to test the moisture content, inside your hard case and a humidifier to control the moisture content in the surrounding air.
How Humidity Affects Acoustic Guitars
Wood is ‘hygroscopic’ which means it increases or reduces moisture content, based on the relative humidity of the current environment.
In a humid environment, the wood of your guitar will absorb moisture and expand. When the climate is dry the guitar loses moisture content and the wood contracts.
Relative Humidity
The relative humidity is the amount of water in the air, relative to the current temperature. It is measured as a percentage of the moisture levels that potentially could be contained in the air at a given temperature.
For example, 70% humidity means the level of moisture is 70% of the total moisture content it could otherwise hold.
Equilibrium moisture content
But it’s not quite that simple when it comes to the ideal humidity level. The age of the timber also comes into play. Typically wood will start losing moisture from the moment it is cut. It will continue to lose moisture until it reaches equilibrium moisture content, meaning it matches the moisture content of the surrounding air.
Once this occurs, the moisture content of the wood will change based on the relative humidity. Up until it reaches equilibrium moisture content it will continue to lose moisture for the most part.
This is one of the reasons, amongst others, people often credit older guitars with having better tone, as the moisture content reduces the guitar becomes more responsive and has greater clarity, at least up until a point.
Humidity and Guitars
Just how much the relative humidity affects your guitar depends on many things, including, as we have already mentioned, the age of the guitar along with the wood it’s built from and how the different types of wood relate to each other (e.g. soundboard and back and sides) and how they handle moisture.
While still a consideration, changes in humidity have less impact on electric guitars due to the thicker lacquer finish seen on most electrics.
Short Term Humidity Issues
In the short term, humidity can affect tuning stability and intonation.
For example, high humidity may affect tuning stability due to the wood expanding or contracting and the neck straightening affecting the string height. In more arid climates fret-related problems are more likely to occur including sharp fret ends (fret sprout).
The other problem is, that an acoustic guitar comprises wood and metal e.g. frets and tuners. As the wood expands or contracts, metal objects such as frets can loosen, causing fret buzz.
Long-Term Humidity Issues
Over the longer term, humidity can cause bigger problems, structurally. Especially if A consistent humidity level is ideal for storing acoustic guitars, but if you live in America’s Southwest, humidity can be as low as 20% during winter and as high as 80% at times in summer. In this kind of environment, some form of long-term guitar humidity control is a must.
Depending on the guitar, large fluctuations like these over time will result in problems, potentially resulting in structural repairs. This includes more permanent changes to the neck and the potential for cracking, warping, and glue joints to fail under tension.
Structural damage is more likely to occur where different sections of wood are joined e.g. the bridge, neck joint, back, sides and top, and headstock. Particularly if the difference in the flexible strength of the joining timbers is not equal.
This is one of the reasons guitars often have a binding strip running around the body of the guitar. Firstly, it protects the hard edges where the timbers join, however, it also reduces moisture absorption along the open grains where the edges meet. Being a more flexible material, the binding allows for some movement at the joint.
Signs of humidity damage on acoustic guitar
- Oxidization of the frets and hardware
One of the earliest signs of a wet guitar is the frets oxidizing. Unlike corrosion, this can usually be cleaned with warm water and a rag or 0000 fine-grade steel wool. - Fret Sprout
One of the first signs of a guitar that is too ‘dry’ is fret sprout. This occurs when the wood of the neck contracts leaving the edges of the frets exposed. If unsure run your hands down the edge of each side of the neck. - Unusually High Action
Fluctuations in humidity will affect the amount of relief or bow in the neck. If the action feels high, or alternatively you are experiencing fret buzz the neck may have been affected by a change in humidity. - Warping (particularly near the bridge)
The soundboard of a particularly dry guitar will begin to cave inwards slightly. While the amount obviously depends on how dry the guitar is, this will affect the height of the bridge, impacting the guitar’s action. - Glue giving way
The bridge is the first place this will appear due to the high tension the bridge is already placed under on behalf of the strings. - Open Seams
Soundboards are book-matched with two matching pieces of wood. Due to wood contracting, these seams may begin to show signs of opening up.
Humidity and Tone
Humidity also affects acoustic guitar tone. Guitars that are excessively ‘dry’ are often described as sounding brittle and thin. There are, of course, degrees to this, but in general, a dry guitar will sound more responsive and brighter than a ‘wet guitar’.
When the guitar is ‘wet’ the tone is often described as muddy and inarticulate as the wood cells expand, and the guitar feels ‘heavier’ and less responsive.
How to Address Humidity when Storing Your Acoustic Guitar
So, now that we have identified the problem, what can be done about it?
Well, the good news is while humidity is something you should be aware of, it’s also not all that difficult to control.
First, consider the area you live in and if the guitar ever leaves home. For instance, if you live in a relatively stable environment with little fluctuation in relative humidity and haven’t noticed a problem with your guitars in the past, humidity is probably not something you need to worry too much about.
Second, consider the materials your guitar is made from. If the guitar is made completely from solid wood e.g. not using laminated timber of any kind it is more susceptible to humidity.
Thirdly, Consider your storage area. Generally speaking, guitarists, who prefer not to leave their guitars lying around on the couch or stashed in a corner have the following options:
- Display cabinet
- Hard case
- Wall Hanger
- Guitar Rack
- Guitar Stand
How you store the guitar will likely depend on how often you play a particular guitar.
I wouldn’t recommend using a guitar stand for anything other than while you are playing the guitar, or anything more and it’s only a matter of time before it gets knocked over.
Otherwise, a hard case (with the lid closed) is the best option as it’s easier to control the humidity within the confined space of the case.
Otherwise, wall hangers and guitar racks (I personally use both) are also good options but you will need to control the humidity of the room rather than just the case.
Measure the Relative Humidity
Your first step should be to measure the moisture content of the air. To do this you will require a hygrometer, which is an instrument used to measure moisture content.
Acoustic guitars should ideally be stored at between 45 – 55% humidity, although closer to the 45% mark is preferable.
Where you place the hygrometer depends on where you store the guitar. E.g. if you store the guitar in a hard case the hygrometer should also be placed in the case.
If however, you have multiple guitars, it may not be practical to keep them all in cases. In which case, if you store your guitar in a room the hygrometer should be placed in the room, near where the guitars are stored.
Highly Rated Acoustic Guitar Hygrometers
MusicNomad The Humitar ONE – Acoustic Guitar Humidifier & Hygrometer
- Made specifically for acoustic guitars
- Includes a humidifier to actively set moisture level
- Slides into soundhole
- Takes readings every 20 seconds
- Rated 4.6 out of 5
Guitto 2-in-1 Humidity Care System for Acoustic Guitar Humidifier Hygrometer GHD-01
- Made specifically for acoustic guitars
- Includes a humidifier to actively set moisture level
- Slides into soundhole
- Analog dial looks sweet
- Rated 4.2 out of 5
Controlling the Humidity
Measuring the relative humidity is of course only half the battle. Next, we need to control the humidity of either your case or the room itself.
To do this we need a humidifier.
When it comes to guitars, humidifiers come in three different types:
- Soundhole humidifier
- In case humidifiers
- Room humidifier
Soundhole humidifiers
As the name implies. Soundhole humidifiers sit within the soundhole, nested between the strings of the guitar.
| Product | Comments |
Music Nomad MN300 Humitar Acoustic Guitar Humidifier  | -Long-lasting. – Quick flip-top for checking the moisture content of the contained sponge. – Highly rated by buyers. |
D’Addario Acoustic Guitar Humidifier  | – Suspended by the guitar strings, avoiding direct contact with the guitar. – Features a non-drip design. – D’Addario is a well-established brand in the music industry |
In-case humidifiers
In-case humidifiers generally come as a sponge in an enclosed case or in the form of in-case humidifiers generally come as a sponge in an enclosed case or in the form of a tube that hangs inside the soundhole of the guitar. In some cases using both is a good option with the encased option better suited to the neck and able to be stored in the pick compartment of the case, while the tube protects the body of the guitar. The D’Addario Humidipak comes with packs for the body and neck.
| Product | Comments |
Dampit Guitar Humidifier Super  | – Protecting guitars since 1966. – Recommended by a number of influential names in the industry. – Includes a soundhole cover that retains moisture inside the guitar body. |
D’Addario Humidipak Automatic Humidity Control System  | Two-Way Humidification System. – Maintains 45%-50% relative humidity. – Adds or removes moisture as required. – Maintenance replacement packs available. |
Room Humidifiers
Room humidifiers are often larger and require electricity because they are required to control the humidity of an entire room compared to a case.
| Product | Comments |
| TaoTronics Cool Mist Humidifier | – Very quiet. – Produces less than 38 dB of noise. – 4L tank. – Can run for 30 hours without requiring refilling in most standard room sizes. – Automatic shutoff when water runs out |
| Morocco Ultrasonic Cool Mist Humidifier | – 6L Tank. – Can run for 60 hours without requiring refilling in most standard room sizes. – Optional night light. – Low water warning light. – Will stop misting if water becomes too low. |
Summary
The effects of humidity are something all guitarists probably need to keep in mind, but unless living in an area with large fluctuations in humidity or you happen to live in a very dry or very wet climate, it’s not something a few silica gel packs kept in your guitar case can’t handle.
If unsure measure the humidity (45-55% Relative Humidity) of your case or storage area and then, if required, use one of the products listed above, set, and for the most part forget.
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