Does Merino Wool Shrink in Cold Water When Washed or in Dryer?

Have you ever invested in a luxurious merino wool garment, only to worry about its fate in the wash? The question looms: does merino wool shrink when washed in cold water or tossed into the dryer?

If you’ve found yourself pondering this dilemma, fear not! In this guide, we’ll uncover the truth behind merino wool’s behavior when exposed to different temperatures and washing techniques.

So, whether it’s a splendid merino wool sweater or a delightful pair of socks that has stolen your heart, you’ll learn whether cold water or the dryer is the real culprit behind shrunken wool.

You will also learn some tips to keep your merino wool items fitting perfectly for many wears to come.

So, does merino wool shrink? Merino wool can shrink when washed or dried improperly. Using cold water, delicate cycles, and air drying helps prevent shrinkage. Higher quality merino wool from reputable brands is pre-treated to reduce felting and shrinkage. Natural, untreated merino is more prone to significant shrinkage when machine washed or tumble dried. Proper stretching while drying and using steam while ironing may help restore size after slight shrinkage. However, felted wool cannot be restored to original size. Overall, following garment care instructions to use cold water, gentle detergent, and air dry will minimize shrinkage risk for most merino wool items.

How Can Merino Wool Shrink?

Let’s discuss the key factor that causes the shrinkage of Merino wool.

Felting of Merino Wool Fibers

The underlying cause of shrinkage in Merino wool is a process called felting. Felting occurs when the outer layer of scales on the wool fibers, known as the cuticle, become interlocked with each other.

Merino wool fibers have an outer cuticle layer consisting of overlapping scales that give the wool a rough texture.

Wool fibers have a cylindrical shape with overlapping scales on the surface. These scales can open or close depending on the temperature and moisture level of the fiber.

When the scales rub against each other from agitation in water, they can catch onto each other and mesh together throughout the fabric.

Once the scales become permanently locked together through this felting process, the wool shrinks and cannot be returned to its original size or shape. The fibers have undergone structural changes at the nanometer scale.

Factors Promoting Shrinkage and Felting of Merino Wool

There are following key factors that promote shrinkage and felting in Merino wool:

  • Agitation: Friction from washing, spinning, or tumbling causes the wool scales to abrade against each other, promoting felting. Machine washing causes more agitation than hand washing.
  • Temperature: Hot water causes the wool scales to open up, making them more prone to catching onto each other. High heat drying can also damage and shrink the wool.
  • Moisture: Water causes the scales to swell, exposed more area for potential felting. Higher moisture content increases shrinkage risk.
  • Untreated Merino wool: Untreated Merino wool is more prone to shrinkage than superwash or treated Merino. The protective treatments on the latter help prevent the scales from locking together during washing and drying. Untreated Merino requires especially gentle machine washing on the wool cycle in cold water, with no tight wringing and air drying flat instead of heat. Even then, some shrinkage may occur over time.

Note: Most felting will not occur in untreated wool fabrics as long as the moisture content stays below approximately 15% by weight. Below this threshold, the fibers are too dry for the scales to properly lock together during agitation. So air drying Merino wool completely until crisp dry helps maximize shrink resistance. Even treated Merino can shrink somewhat in damp conditions.

Superwash Merino Resists Shrinkage

Superwash Merino wool has been treated to remove the outer cuticle scales or to coat the fibers to prevent scale bonding. Common methods include:

  • Acid washing to etch the scales.
  • Coating fibers with resin to fill in scales.
  • Plasma treatment to oxidize the outer cuticle layer.

This prevents the scales from interlocking, greatly reducing shrinkage compared to regular untreated Merino wool. However, some shrinkage can still occur if exposed to high heat drying.

Merino Wool Fiber Structure

The complex structure of Merino wool fibers influences their shrinkage behavior:

  • Merino wool consists of a complex protein composition including amino acids like cystine.
  • The outer cuticle layer contains overlapping scales giving the fibers a rough texture. The scale structure facilitates felting shrinkage when agitated in water.
  • Inner cortical cells give the wool natural crimp and strength. Discontinuities can increase chances of fiber breakage.
  • Absorbed moisture makes the fibers more elastic and easier to deform, though they fully recover their shape if stretching is under 30%.
  • Covalent bonds between proteins and crosslinks give wool hardness and shape resilience. Cleavage of bonds by treatments like plasma can reduce felting.

How to Wash Merino Wool To Prevent Shrinkage?

Merino wool is prized for its softness, warmth, and odor-resistant properties. However, one downside is that it can easily shrink if not washed properly. Here are some tips for washing merino wool to minimize shrinkage:

Hand Washing Is Best

Machine washing, especially in hot water, puts merino wool through agitation that can cause felting and shrinking of the fibers.

For this reason, hand washing merino wool items is highly recommended. Use a gentle wool wash or a mild liquid laundry detergent.

Soak the item in cold water, then squeeze out excess water without wringing or twisting.

Use Cold Water

Hot water, over 30°C/86°F, should always be avoided to washing Merino wool clothing as it causes the scales on the wool fibers to bond together resulting in shrinkage.

Cold water under 30°C/86°F is less likely to felt the fibers. Avoid sudden temperature changes too as going from hot to cold can shock the fibers.

Machine Washing Is An Option

If hand washing isn’t possible, the washing machine can be used on the wool or delicate cycle in cold water.

Make sure to use a mild, wool-safe detergent. Don’t overfill the machine. Remove promptly and lay flat to air dry without heat. Some shrinkage may still occur.

Gentle Detergents Are Best

Look for natural, low-sudsing detergents made for wool. Avoid regular detergents with optical brighteners or surfactants that can damage fibers.

Woolwash or Eucalan are gentle liquid detergents that work well. Only use a small amount and rinse thoroughly to prevent residues that affect the fibers.

Don’t Use Fabric Softener

Fabric softener coats the wool fibers, interfering with their natural properties like wicking and insulation. It should always be avoided. The lanolin oil in merino wool provides enough softness once it’s clean.

Wash When Needed, Not Frequently

Merino wool is naturally odor and bacteria-resistant, and doesn’t need to be washed after every wear like synthetic fabrics. Air out worn merino wool items to remove smell before next use. Washing decreases the fibers’ lifespan over time.

Also Read: Merino wool vs synthetic base layers

How to Dry Merino Wool To Prevent Shrinkage?

Follow these tips and your merino wool items will maintain their shape and size wash after wash.

Air Drying is the Safest Method

Without a doubt, air drying is the best way to dry merino wool and prevent any shrinkage.

Since it is the heat from drying that causes the fibers to tighten up and shrink, avoiding heat altogether eliminates that risk.

  • Hang or lay garments flat to air dry. Use hangers or a drying rack. Laying flat prevents stretching out of shape.
  • Air drying may take longer than machine drying but ensures no shrinkage.
  • Place in a well-ventilated area out of direct sunlight. Sun can damage fibers.
  • Merino wool dries quickly even without heat due to the fiber’s moisture wicking properties.

So, if keeping your merino pieces the exact same size is important, air drying is the way to go. It totally prevents shrinkage.

Machine Drying Requires Caution

Machine drying merino wool is possible but risks shrinking if you are not extremely careful. Follow these precautions if machine drying:

  • Use the lowest heat setting possible. High heat causes severe shrinkage and felting.
  • Remove items immediately once dried to prevent over-drying. Set a timer as a reminder.
  • Check on progress frequently to avoid over-drying. This may require stopping and restarting the cycle.
  • Add a couple of clean tennis balls to the dryer. The pounding helps maintain the wool’s shape.
  • Consider putting your merino pieces in a mesh garment bag. This prevents excess agitation.
  • Lay flat or hang to air dry the last bit of dampness. The final drying stages are when shrinkage is most likely.

Again, air drying eliminates any risk of shrinkage from machine drying. But if you must use the dryer, these tips will help reduce shrinkage.

Stretch and Reshape While Damp

Whether air or machine drying your merino wool, you can help prevent shrinkage by gently stretching and reshaping the items while still slightly damp.

  • Lay garments flat and gently pull to desired measurements. Use your hands to shape areas like sleeves and side seams.
  • Hold the stretched shape for 20-30 seconds so it sets.
  • Pins, tape or weights can help hold the desired shape as it finishes drying.
  • This stretching and shaping allows the merino wool fibers to conform to the correct dimensions as they dry.

Reshaping the merino wool pieces while damp allows you to control where shrinkage occurs rather than leaving it up to chance. Combined with air drying, it helps maintain the size and fit.

Other Care Tips To Prevent Merino Wool Shrinkage

Here are some other tips to prevent Merino wool shrinkage:

Washing Merino Wool Separately

One important tip for preventing Merino wool shrinkage is to wash it separately from other clothes. Merino wool is very delicate and can easily be damaged or snagged by zippers, buttons, and other items in the wash.

It’s best to wash Merino in its own load using a gentle wool wash cycle with cold water. This ensures the Merino wool fibers aren’t rubbed against rough or abrasive fabrics that could cause felting or merino wool pilling.

Velcro and zippers on other clothes can snag and damage merino wool. So, keeping them separate during washing and drying is important.

Washing Merino separately also prevents odors or chemicals from other clothes transferring onto the wool items.

Avoiding Fabric Softener and Bleach

When washing Merino wool, it’s important to avoid using fabric softener or bleach, as these chemicals can potentially damage or coat the wool fibers.

Fabric softener leaves a residue that can clog up the natural lanolin and oils in the wool that keep the fibers water-resistant and help the fabric retain its breathability and warmth.

Bleach is also too harsh for delicate wool fibers and can cause them to felt or shrink. Stick to a gentle wool-specific detergent and cold water when washing Merino to maintain the integrity of the fibers.

Higher Quality Merino Resists Shrinkage Better

Not all Merino wool is created equal – higher quality Merino from reputable outdoor brands like Smartwool, Icebreaker, and Patagonia is processed to be more resistant to shrinking and felting compared to lesser quality or unknown branded Merino.

Premium Merino fibers are often treated with chemicals or processes that stabilize the scales on the wool fibers so they don’t interlock and shrink as much when washed.

Lower quality Merino may shrink substantially even with careful washing, while higher end options are more likely to maintain their shape and size. It’s worth paying more for Merino you can wash over many years.

Merino/Poly Blends Shrink Less than Pure Merino

Another way to make Merino wool more resistant to shrinkage is to blend it with synthetic fibers like polyester.

A 50/50 Merino/polyester fabric will shrink less than 100% pure Merino wool when washed because the addition of the synthetic fibers stabilizes the scales on the wool without compromising the natural benefits.

Look for Merino blends rather than pure wool if you want something hardwearing that minimizes shrinkage potential with regular washing.

Make sure to still follow label care instructions when washing Merino wool blends to avoid shrinkage.

Heavier Merino Shrinks Less than Lightweight

Not only does higher quality Merino shrink less, but thicker, heavier styles of Merino wool are also less likely to shrink compared to very lightweight Merino garments.

Heavier Merino has longer, more robust fibers that don’t felt and interlock as easily when washed.

Thinner Merino is more prone to shrinkage because the shorter, finer fibers have more opportunity to move around and shrink up during the agitation of washing.

When choosing Merino layers, opt for mid-weight or heavyweight options if minimizing shrinking is a concern.

Also Read: Best Merino wool hoodies

European Merino Shrinks Less than Chinese Merino

There can also be differences in shrinkage potential based on where the Merino is sourced from.

In general, Merino wool from Europe (commonly Australia, New Zealand or Italy) undergoes more rigorous processing to stabilize the scales and will shrink less after laundering compared to Merino wool from China.

European Merino is generally of higher quality with longer, stronger fibers, while Chinese Merino is more prone to felting and shrinking substantially over time with regular washing.

While Chinese Merino is often more affordable, it may cost more in the long run if it doesn’t hold up to laundering.

Wash in Layers Inside-Out

When washing Merino sweaters, shirts or other layered items, turn each piece inside-out and wash one layer at a time. This prevents the outside fabric layers from rubbing against inner layers that may have a smoother finish like wool lining or silk.

Friction between differing wool weights or fabrics can cause pilling or shrinkage. Washing in layers with plenty of room to move helps the fibers glide smoothly without interlocking or shrinking.

Turning items inside out also prevents insignia or prints from transferring or fading onto other layers during the wash cycle.

Size Up For Brands Like Kuiu That Run Small

Some Merino brands, especially Kuiu, are known for running small. It’s a good idea to size up one size from your normal when purchasing these brands to allow for any initial shrinkage and retain a comfortable fit after multiple washes. This helps the garment maintain its intended size instead of potentially becoming too tight.

Dealing With Shrunken Merino Wool

If you’ve accidentally shrunken a Merino wool sweater in the wash, don’t despair – there are some things you can try to stretch it back out.

1. Soaking the Merino wool item in a diluted hair conditioner solution

One of the most common methods suggested is soaking the wool item in a diluted hair conditioner solution. Conditioner works wonders on wool because it helps relax and soften the fibers.

To try this method, mix a generous amount of conditioner with lukewarm in a bowl or plastic tub.

Submerge the shrunken wool and let it soak for 30 minutes. The conditioner will permeate the fibers and allow them to stretch more easily. Gently pull and stretch the fibers as it soaks.

Once finished soaking, squeeze out excess moisture and lay the wool flat to air dry completely. Stretch it periodically as it dries.

Steaming With Iron

Another option is steaming with an iron. Lay a damp cloth over the wool item and use a steam iron on a low heat setting just to add moisture back into the fibers. As you steam, gently stretch the fibers into shape.

Be very careful not to directly touch the iron to the wool or you could scorch it. Let the item air dry fully after steaming. The heat and moisture from steaming can reactivate the wool’s natural elasticity.

Try Re-stretching While Damp

No matter which method you use, the key is to stretch the fibers as much as possible while re-dampening and drying the wool.

Pull the material from all angles, focusing on areas that have tightened or bunched up due to shrinking.

Lay flat and use pins, clothespins or folding to maintain the stretched shape through drying. Check on it periodically for full stretching as it dries. 

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