Caveat Emptor!

When is "Superfine" merino not Superfine Merino?

All over outdoor-related web forums you'll see complaints about the itchiness of what the buyers thought was supposed to be "Superfine" and even "Ultrafine" merino baselayer, as this is how the brand they bought described their merino garments.  As these people then assumed all merino would be the same, we thought we should look in to this.

We bought samples of the brands mentioned in the complaints and commissioned an independent analysis and report from New Zealand's AgResearch.  They in turn passed the samples on to New Zealand's Wool Testing Authority.  These are  their findings.

Of the 6 samples sent, all of which claimed to be either "superfine" or "ultrafine" merino:

• 2 samples were so coarse as to fall completely outside the Australian and New Zealand merino classification system.
• 2 samples were "fine", not ultrafine or superfine
• 2 samples were technically superfine, but of these, one sample included such a high percentage of coarse fibres that it was liable to be itchy.
• None of the samples was "Ultrafine" merino in terms of the merino fibre classifications used in Australia (Australian Superfine Wool Growers Association 2003).

We have now passed the full report on to Trading Standards and Advertising Standards, as we believe the findings warrant investigation and proper regulation.

In  the meantime, it is worth remembering:

1. Genuine superfine NZ Merino is rarer than cashmere, so it cannot come at a cheap price. 
2. Ultrafine merino is not only even rarer but is rarely used on it's own as it is not strong enough to take much wear and is more often used mixed with other fibres for baby and fashion wear.
3. Few of us if any would be able to tell the difference in "feel" between ultrafine and superfine merino anyway
4. Even a technically "superfine" fabric can itch if it contains more than a small percentage of coarse, i.e. over 30 micron fibres.

The Technical Bit

The measurements of the samples were analysed using the OFDA technique which measures the mean and distribution of the fibre diameter of wool using an optical fibre diameter analyser (OFDA). 

• The mean fibre diameter (MFD) is the arithmetic average diameter of all the fibres scanned.  
• The coefficient of variation (CV) is the standard deviation expressed as percentage of the mean and is a simple indication of the variability of fibre diameter in the sample

For a particular fibre to cause prickle, its buckling load must exceed the force at which certain nerves in the skin are triggered.  Buckling load of an individual fibre depends on its diameter and free length.  Diameter is the most powerful influence, and researchers have established that the amount of coarse fibre present (e.g. the percentage of fibres greater than 30 micron in diameter) is a key parameter.  A fabric with a low MFD may or may not be prickly, depending on how much coarse fibre is present. Fibre that is suitable for next-ro-skin wear is likely to have a low MFD, but should also have a low CV and small percentage of fibre at the coarse end of the diameter distribution.