Ultra Zip - Big Heart Adventures

Fabric Guide

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The Women's Ultra Zip Base Layer top is as soft and comfortable as ever combining all the natural benefits of our finest MicroMerino® fabrics with just enough nylon to create our most durable fabric ever to withstand the most demanding adventures

Designed with Ultra Runners in mind we made it extra comfortable and extra durable. Made with lightweight 83% superfine Australian Merino Wool, 12% Nylon for durability and 5% Elastane for an easy four-way stretch and freedom of movement. Still Merino-rich, and perfect for adventure racing and what in Australia, we like to call ‘bush bashing’.  The sporty fit is streamlined, but not ‘contact fit’ like the Altitude Base Layer Range.

It is the ultimate in versatility and temperature regulation; roll the sleeves up, and pull the zip down when it’s mild and pull the sleeves down, zip up and thumb loops on when the temperature drops. Wear it on its own to stay cool in warm or mild weather, or as part of a layering system when the temperature drops.

This Base Layer is packed with extra performance features like tag-free labels and flatlock stitching helps eliminate chafe and maximize comfort. The high collar and ¾ zip add greater temperature regulation, while the thumb loops keep your hands warm and stop your sleeves riding. The reflective trims have been added for extra safety in low light.

Designed with a body-skimming, sports fit. True to size.

Print to order. Exclusive Big Heart Adventures limited edition print. 

Lightweight 160gsm

83% superfine Australian Merino Wool

12% Nylon for extra durability

5% Elastane for an easy all-way stretch



Customer Reviews

Based on 34 reviews
Lyn Mackaway (Newcastle, AU)

This is a great long sleeve merino top to wear when hiking in cooler weather. Very soft merino, so no skin irritation.

Carmen Grzesik (Adelaide, AU)
Came back for more !

I took this top and a Universal Tee with me hiking in Slovenia late August. Both were so good on the trail ( kept me cool while hiking and
warm at night, and didn't get smelly after several days) that I bought another of each. They worked just as well in the drizzly chilly Spring weather Adelaide's having at the moment.

Kaye Potter (Melbourne, AU)
Love this garment

This is my second purchase of this style. I love the wool next to my skin in all weathers. I love the square shoulder design. I love the cherry red colour.

Barbara McKay (Queanbeyan, AU)
Perfectly Ultra

IO ultra zip is perfect - aI live it as a layer in the Canberra cold, warm, soft and love the green.

Heather Parkes (Adelaide, AU)
Very comfortable

Great for layering, also got one as a gift for sa friend and she loved it too. Have several colours now

Clare Dixon (Canberra, AU)

Excellent quality Nice fit Keeps me warm & wicks away moisture


Fabric Guide

While Merino is an amazing natural fibre, not all Merino fabrics are created equal. At ioMerino, we make our own fabrics, using only the best quality fibres, and to very specific specifications that make the most of the natural benefits of Merino. All of them are 'Merino rich’. No cheap blends passed off as Merino. No cheaper scratchy fibres or synthetic substitutes to save money. No unethical production. And each fabric is made for a specific purpose. So if you see something with a small amount of elastase or nylon added, you can be sure it absolutely needs to be there to enhance the natural stretch and durability. 

It took every bit of our 140 years of experience in the wool industry to perfect our fabrics, but we think you’ll agree the end result was more than worth the effort.

Ethically Made. Ethically Sourced. Perfectly Natural. 


Altitude / Zodiac

Lightweight 170gsm 96% Australian Merino Wool with 4% elastane for extra stretch and comfort. A MicroMerino® Fabric. 


Ultra / Universal

Lightweight 160gsm 83% Australian Merino Wool blended with 12% nylon blended for extra durability and 5% Elastane for stretch and comfort.



Midweight 265gsm 96% Australian Merino Wool with 4% elastane for extra stretch and comfort. A MicroMerino® Fabric. 


Summerino - Celsius 

Made from 45% ultra fine MERINO (Ultra Lightweight 150gsm), 45% natural TENCEL (made from sustainably grown wood fiber), and 10% nylon for extra durability. 


Summerino - Keystone 

Ultra Lightweight 150gsm 100% Australian Merino Wool. A MicroMerino® Fabric. 


Merino Compression

Midweight 280gsm 76% Australian Merino Wool, 15% Elastane and 9% Nylon for extra stretch and compression properties.



Ultra lightweight ribbed 155gsm 100% Australian Merino Wool. A MicroMerino®  Fabric. 



Outer Weight 280gsm Fleece 100% Australian Merino Wool. MicroMerino®  Fabric. 



Midweight 260gsm 100% Australian Merino Wool. A MicroMerino®  Fabric. 



Midweight 260gsm waffle texture 100% Australian Merino Wool. A MicroMerino®  Fabric. 


Stride / Glacier / Velocity

Midweight 255gsm French Terry 100% Australian Merino Wool. A MicroMerino®  Fabric. 


Natural Merino Wool benefits: