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Merino Wool Shirts

A review of lightweight long sleeve merino wool shirts from Smartwool, Ibex, Icebreaker, Merino Skins, and WhisperWarm.


by the Product Review Staff | 2003-09-29 03:00:00-06


In the past year, merino wool shirts are capturing an increasing market share, primarily in response to customer desires for less stink, less itch, less clamminess, and more utility over a wider temperature range. These latter advantages of merino wool over polyester and polypropylene synthetics add up to merino wool's greatest advantage: better comfort when worn next to skin.

We've addressed the utility, performance, and technical advantages of merino wool in great detail elsewhere (see [page 00069]Clothing and Sleep Systems for Mountain Hiking[/page]). In the original version of that discussion, which appeared here in 2001, we noted that the customer had few options from which to choose when shopping for merino wool base layers. In fact, the U.S. market was limited to only one serious player: a midweight merino wool shirt from Smartwool.

At that time, we made an aggressive call to manufacturers to develop ultra-thin merino wool garments made with superfine fibers (i.e., fibers less than 18 microns in diameter) that dried faster, offered a wider temperature range, and weighed less than their midweight counterparts. This review highlights some of the fruits of this "merino wool diet" over the past few years. Keep in mind, our review doesn't compile every long sleeve lightweight merino base layer on the market. We've tried to give you a cross-market snapshot of a variety of garments with particular strengths that would appeal to a wide audience.

Garments Reviewed

Long Sleeve Zip-T Shirts

  • Smartwool Trad
  • Icebreaker Ryder
  • WhisperWarm Zip-T

Long Sleeve Crew Shirts

  • Smartwool Aero
  • Merino Skins Crew
  • Icebreaker Skin
  • Ibex Outback
  • WhisperWarm Crew

Review Criteria

Weight. Weight of each crew in a size men's or unisex medium was measured on a NIST-certified and calibrated scale and reported to the nearest 0.1 ounce (3 g).

Price. Price is reported as currently available average market prices from online retailers. Where appropriate, prices were converted from international currencies to USD using the currrency calculator at

Fabric Weight. Fabric weights, with the exception of the Smartwool Trad (which we consider to be a "midweight" fabric), are all in the range of 6 oz/sq.yd. (200 g/sq.m.). Fiber diameter was verified to be less than 20 microns for all garments, thus meeting the specification for "Superfine" merino wool. Thus, we classify all of the other garments as "lightweight" using the conventional scale of baselayer fabric weighting of "light-mid-expedition" weight.

Sizing. Sizing is identified as "true" for garments that meet U.S. sizing conventions; sizing is indicated as "1/2 size small" when the specified size is one half size smaller than U.S. sizing conventions, and as "full size small" when the specified size is a full size smaller than U.S. sizing conventions. These sizing grades were based on user perception of fit as well as measurements taken of arm length, neck hole diameter, torso diameter, and hem length.

Fit. Fit grades are assigned on a sliding scale, starting with the tightest fits: tight, snug, trim, loose, or baggy, with "trim" identifying our perceived ideal for base layer garments, providing a good balance of mobility, volume, breathability, and ventilation.

Comfort of Fit. The comfort of fit grade (on a scale of 1 to 5, with 1 = worst and 5 = best) is not based on the sizing grade assigned above. Rather, the criteria considers the freedom of mobility, a balance of trim vs. baggy fit, length of hem, and comfort of wrist and neck closures. This is a subjective rating based on user perception.

Warmth. Scale of 1 = coldest and 5 = warmest. This criteria is evaluated on a combination of fabric thickness and construction combined with tightness of fit. Thicker fabrics get "warmer" grades, as do "more trim" fitting garments.

Ventilation. 1 = poor ventilation and 5 = excellent ventilation. Ventilation is based on the availability of a neck zipper, fit (see fit criteria above), and size of neck, hem, and cuff openings.

Breathability. 1 = poor breathability and 5 = excellent breathability. This criteria is based on fabric thickness and knit construction. Fabrics with more porous and thinner structures are assigned higher breathability grades. Typically, but not absolutely, breathability and warmth are inversely related.

Value. 1 = high cost/performance ratio, 5 = low cost/performance ratio. Value is based on cost in combination with features, fit, and versatility of the garment.

Note: Zip-T and crewneck shirts were graded in separate groups, and numerical ratings should not be compared between the two styles.

Review Summary

The following table provides a summary of the review.

Brand Style Model Weight (oz) Weight (g) Price Fabric Weight Fit Sizing Comfort of Fit Warmth Ventilation Breathability Value
Smartwool long sleeve zip-t Trad 9.5 269 $75 Mid loose true 3.5 4.5 5.0 3.0 3.0
Icebreaker long sleeve zip-t Superfine (Ryder) 8.1 230 $95 Light trim 1/2 size small 4.5 4.0 4.0 4.0 2.0
WhisperWarm long sleeve zip-t n/a 5.8 164 $66 Light snug full size small 3.5 2.5 3.5 5.0 4.0
Merino Skins long sleeve crew n/a 5.8 164 $32 Light snug 1/2 size small 3.5 2.5 3.0 5.0 5.0
Smartwool long sleeve crew Aero 7.2 204 $60 Light trim true 5.0 3.5 4.0 4.0 3.0
Icebreaker long sleeve crew Skin 5.9 167 $51 Light tight 1/2 size small 3.0 3.0 2.0 5.0 3.5
Ibex long sleeve crew Outback 7.2 204 $78 Light trim true 5.0 3.5 4.0 4.0 2.0
WhisperWarm long sleeve crew n/a 4.6 130 $50 Light snug full size small 3.5 2.0 3.0 5.0 3.5

Review Summary

All of the shirts reviewed herein are well-constructed and durable with high quality merino wool fabrics. Differences in shirts are seen primarily in garment fit, fabric thickness, and fabric porosity. These three features in turn affect garment warmth, ventilation, breathability, and comfort.

With this in mind, we did feel that three garments in particular stood out from the rest. The first was the Ibex Outback shirt, which gets style points for its exceptional fit and deserves an honorable mention.

We also found somewhat of a sleeper in the long sleeve crew from Merino Skins. At $32, it provides the best performance-to-value ratio of any shirt in the review, and it used the most porous fabric of the lot. Its only caveat was that sizing ran small and the fit was a little snug (with short arms and a short hem), so be sure to size up one full size from your normal size. Merino Skins products are available from

Finally, we felt that the Smartwool Aero crew earned top honors as the best all-around merino wool base layer shirt in terms of fit, weight, and overall performance. An excellent fit that wasn't too baggy or snug, combined with a lightweight fabric that made the shirt suitable for year-round conditions (this was the most comfortable shirt tested in temperatures exceeding 80 degrees in the dry climate of the Northern Rockies), and a sticker price that was almost $20 less than the Ibex product made it a clear favorite among our reviewers.

What's Coming?

Merino wool fabrics are continuing to evolve. From here, we encourage manufacturers to pursue the development of merino wool-synthetic blends (the addition of synthetic fibers can increase durability and improve water absorption, as well as maximizing fabric memory, or its resistance to permanent, or "plastic" stretching). In addition, we'd like to see some of the international garment manufacturers (especially those from New Zealand and Australia) recognize sizing conventions that better reflect a need for outdoor performance - including longer sleeves and hems.

Around the Corner: We are currently reviewing a new shirt, the Ibex Pacifica. At the same 7.2 oz (204 g) weight as the Outback, the Pacifica has a deep (10 in, 25 cm) neck zipper, hand warmer cuffs and trim fit. First looks indicate that this full-featured wool top offers a lot of bang for the buck, and initial field reports indicate that it offers excellent fit and comfort.


"Merino Wool Shirts," by the Product Review Staff. (ISSN 1537-0364)., 2003-09-29 03:00:00-06.