Merino Wool Shrinkage: Causes and How to Prevent it

As someone who loves clothing made from merino wool, I was devastated the first time I pulled my favorite sweater out of the dryer only to discover that it had shrunk to the size of a toddler’s shirt.

Based on my research, I understand this is a common and frustrating problem and one that’s caused many wool enthusiasts to throw their hands up in defeat.

But what causes merino wool shrinkage, and is there anything we can do to prevent it?

In this blog post, we’ll dive into the science behind merino wool fibers, explore common mistakes that cause shrinking, and equip you with foolproof tips on how to prevent it from happening.

Merino wool shrinkage causes and fixing

Causes of merino wool shrinkage

Merino wool has many benefits, which make it popular for clothing. 

It is a high-quality type of wool that is valued for its softness, warmth, and moisture-wicking properties. However, one common issue that many people experience with merino wool is shrinkage.

In this section, I will discuss the natural properties of wool fibers and how these properties affect merino wool specifically.

I will also look at the factors that contribute to the shrinkage of clothing made from merino wool.

Natural properties of wool fibers

Merino wool is a natural fiber that is composed of a protein called keratin that forms the wool’s complex structure of scales and fibers, which give it a natural crimp or waviness.

This crimp gives wool its characteristic elasticity and resilience as well as its ability to trap air and insulate against cold temperatures.

Additionally, wool fibers have microscopic scales on their surface, which can interlock with one another when exposed to moisture or heat.

When wool is exposed to moisture, the scales on the surface of the fibers can swell and interlock causing the wool to shrink and become felted.

This felting occurs because the interlocking of the fibers causes them to become shorter and tighter resulting in a reduction in overall size.

In addition, heat can cause the scales to open up further and interlock more tightly, exacerbating the shrinkage.

How does this apply to merino wool?

Merino wool, in particular, is known for its fine, soft fibers, which have a smaller diameter than many other types of wool.

While this gives merino wool its unique softness and drape, it also makes it more susceptible to shrinkage.

This is because the finer fibers have a higher surface area-to-volume ratio, which means that there are more scales on the surface of each fiber that can interlock and cause shrinkage.

Factors that contribute to the shrinking of merino wool clothing

Merino wool, like all wool, is prone to shrinkage when exposed to certain conditions. The main cause of merino wool shrinkage is the application of heat, agitation, and moisture.

1. Heat

As I stated earlier, merino wool fibers have small natural scales that can interlock and cause matting or felting when exposed to certain factors.

One of these factors is heat.

Does Merino wool shrink?

When heat is applied to the wool, the scales become compressed and lock together more tightly causing the fibers to shrink.

This is why it’s important to avoid exposing merino wool clothing to high temperatures.

For example, I’ve seen people accidentally shrink their merino wool sweaters by washing them in hot water or putting them in the dryer on high heat.

The heat causes the wool fibers to contract, and the fabric becomes shorter and tighter. As a result, the sweater no longer fits properly and may even feel scratchy and uncomfortable.

In some cases, the shrinkage was so severe that the clothing was no longer wearable

Another example is when people iron their merino wool clothing at high temperatures. The heat from the iron causes the fibers to compress and shrink leaving the clothing distorted and misshapen.

2. Moisture

Another factor that causes the shrinking of wool clothing is moisture.

Merino wool fibers have a natural tendency to absorb moisture, which can cause them to swell and become more pliable.

When the fibers are agitated or stretched while wet, they can become compressed and lock together causing the fabric to shrink.

For instance, washing your merino wool clothing like socks in water that’s too hot or leaving it to soak for too long makes them susceptible to shrinkage.

The reason for this is that the excess moisture causes the wool fibers to swell and become more susceptible to damage and compression, which can lead to shrinking.

Another example is when people wear their merino wool clothing while exercising or sweating heavily.

The moisture from sweat can cause the wool fibers to swell and compress leading to shrinkage and distortion.

3. Agitation

Agitation, or the act of rubbing, twisting, or stretching wool fibers, can cause them to become compressed and lock together, leading to shrinkage.

When merino wool clothing is agitated during washing, drying, or ironing, the fibers can interlock and become compressed, resulting in a tighter and shorter fabric.

For example, if you accidentally throw your Merino wool sweater into the washing machine with your regular laundry and add a high spin cycle, it is likely to shrink.

The vigorous spinning and rubbing action of the washing machine can cause the wool fibers to rub against the other clothes leading to compression and interlocking of the fibers.

Also, shrinking can occur when you hand wash your Merino wool clothing and use a rough scrubbing motion to clean the fabric.

The agitation caused by the rough scrubbing can cause the wool fibers to become tangled and interlocked leading to shrinkage, deformation, or distortion.

This is why it is recommended to use gentle washing methods and avoids subjecting Merino wool clothing to mechanical stress or agitation.

4. Alkaline detergents

Alkaline detergents can cause merino wool clothing to shrink by damaging the fibers and causing them to lose their natural elasticity.

Wool fibers are sensitive to pH levels and exposure to high-pH detergents can break down the fibers and cause them to become weaker and more susceptible to damage.

Most people are not aware that wool wash detergents should have a mild or neutral PH and should not contain whiteners, bleach, or stain removers.

A few years ago, I was part of ‘most people’ (please don’t judge me). So, I washed my Merino wool scarf with a regular laundry detergent that contained bleach and other harsh chemicals.

After the wash, the scarf had shrunk and become misshapen and the wool fibers felt stiff and scratchy.

I later learned (I’m always learning from experience) that the alkaline detergent had caused damage to the wool fibers leading to shrinkage and loss of elasticity.

Washing wool clothing with detergents containing harsh chemicals also damages the wool fibers and makes them susceptible to shrinkage.

How to prevent merino wool from shrinking

From my experience, merino wool clothing can shrink easily if not properly cared for.

So, here are some things you should do to prevent shrinkage.

  • Always read the care label

Before washing your new merino wool sweater, socks, hat, or scarf, check the care label to see if there are any specific instructions.

can merino wool be washed in the washing machine?

Some merino wool items may require hand washing or delicate machine washing while others may need to be dry cleaned.

  • Use cold water

When washing merino wool, I always make sure to use cold water. As we’ve seen, hot water can cause the fibers to shrink and lose their shape.

If machine washing, run a delicate cycle with cold water and use a laundry bag or pillowcase to protect the garment from snagging or stretching in the machine.

Additionally, avoid using the dryer and instead air-dry your wool clothing.

  • Use a gentle detergent

Acidic and alkaline detergents damage the wool fibers and cause shrinkage.

So, it’s advisable to use a gentle detergent with a mild detergent that is specifically designed for wool and other delicate fabrics.

If hand washing, I’ve found that using a wool-specific detergent like Woolite works well. Gently agitate the garment in the water, but be sure not to scrub or twist it too vigorously as this can cause it to shrink.

Also, avoid using fabric softener or bleach as these can damage the wool fibers.

  • Don’t wring or twist

When washing and drying your merino wool, it’s important to handle the fabric gently.

Avoid wringing or twisting the fabric as this can cause it to stretch and lose its shape.

Instead of wringing or twisting, I recommend gently pressing out the excess water from the fabric using your hands or rolling the item in a towel to remove any excess moisture.

  • Don’t use a dryer

When it comes to drying, never put your merino wool garment in the dryer. Instead, lay it flat on a clean, dry towel to air dry. This will help it maintain its shape and prevent it from shrinking.

Also, avoid hanging your merino wool garment to dry as this can cause it to stretch out of shape.

I’ve had some personal experiences with merino wool shrinking, and it’s not a pleasant sight!

Once, I accidentally put my merino wool sweater in the dryer, and it shrank to half its original size.

I learned my lesson the hard way and now always make sure to follow the care instructions carefully.

  • Store properly

When storing merino wool items, make sure to fold them neatly and store them in a cool, dry place away from direct sunlight.

Also, hanging merino wool items for long periods can cause them to stretch out of shape, so it’s best to avoid hanging them.

If you need to hang them temporarily, I recommend using padded hangers or folding them over the hanger to prevent stretching.

It’s also a good idea to store your merino wool items separately from other clothing items as rubbing against other fabrics can cause pilling and damage to the fibers.

Frequently asked questions 

  • Can merino wool be stretched back after shrinking?

Yes, merino wool can be stretched back into shape to some extent after shrinking. However, the extent to which it can be stretched back depends on several factors such as the degree of shrinkage, the specific type of merino wool, and the garment’s construction.

  • Can merino wool be safely washed in a washing machine?

Yes, merino wool can be safely washed in a washing machine, but it’s important to take some precautions to avoid shrinkage and damage to the fibers. Before washing your merino wool item in a washing machine, be sure to read the care label to see if the item is machine washable.

  • How much does wool shrink?

The amount of wool that shrinks depends on several factors, including the type of wool, the specific garment, and the care instructions followed. So, the degree of shrinkage varies, but in some cases, wool garments can shrink up to one size or more.

  • Can you put merino wool in the dryer?

It’s generally not recommended to put merino wool in the dryer as the heat and agitation can cause the fibers to shrink and lose their shape. Instead, it’s best to air-dry merino wool items by laying them flat on a clean towel in a cool dry place away from direct sunlight or heat sources.

  • Does merino wool shrink when dry cleaned?

Yes, merino wool may shrink when dry cleaned if the dry cleaner uses high temperatures or harsh chemicals during the cleaning process. If you want to dry clean, check the care label to see if the item is labeled as dry clean only, and then choose a reputable dry cleaner who specializes in wool or delicate fabrics.

  • Does merino wool shrink in hot water?

Yes, merino wool can shrink in hot water. Wool is a natural fiber that tends to shrink when exposed to high temperatures. This is because the heat coupled with agitation and friction during washing can cause the fibers to compress and tighten leading to shrinkage.


In conclusion, merino wool is a luxurious and versatile fabric that requires proper care to maintain its quality and shape.

However, in our recent article, one of the potential drawbacks of merino wool we highlighted was its tendency to shrink when exposed to heat and agitation.

So while merino wool is less prone to shrinkage than other types of wool, it can still shrink if exposed to high temperatures, harsh detergents, or excessive agitation.

To prevent shrinkage and extend the life of your Merino wool items, it’s important to follow the care instructions on the garment’s label, avoid washing it using hot water and air dry it by laying it flat on a clean towel.

You can also consider trying other alternatives to merino wool that are low maintenance. 

But generally, by taking proper care of your Merino wool items, you can enjoy their softness, warmth, and durability for years to come.

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