Ask a uniform supplier how long a blazer should last and you will usually be told it is hard-wearing. That word carries no information. It is not a lie, exactly, it is just an adjective standing in the place where a measurement should be, and after twenty years of reading test reports I have stopped accepting it. Durability is a laboratory quantity. Somebody either measured it or did not.
What the lab actually does
Four tests carry most of the weight. Abrasion resistance is measured by the Martindale method under ISO 12947: a disc of the fabric is rubbed in a figure of eight against a standard abradant, and the machine counts cycles until threads break. Tear and tensile strength measure the force needed to rip the fabric and to pull it apart. Seam slippage measures the load at which a sewn seam starts to open and the stitching pulls through the weave. Colourfastness measures how much dye survives washing and rubbing, which is the difference between a blazer that looks tired at Christmas and one that does not.
Why one number can mislead you
A fabric can pass forty thousand Martindale cycles and still produce a garment that fails in a term, because a garment is not a fabric. It is a fabric plus seams plus a lining plus a fastening, and it fails at whichever of those is weakest. The blazer that comes back to us is almost never worn through at the elbow. It has a lining torn at the armhole, or a pocket that pulled away. Any supplier quoting you an abrasion figure and nothing else is quoting you the strongest link.
There is a second problem, and WRAP's Clothing Longevity Protocol exists partly to address it. Most durability testing is done on virgin fabric that has never been washed. That is not the condition the garment spends its life in. Wash and wear testing runs the same measurements after twenty or thirty domestic cycles, and the ranking of fabrics can change completely once you do, because some finishes that deliver excellent numbers on day one are essentially gone by wash fifteen. If someone shows you a test report, the useful question is not what the number was. It is what the fabric had been through before the number was taken.
The rules that will force this into the open
Textiles are the top priority group under the EU's Ecodesign for Sustainable Products Regulation, and durability requirements including tear strength, tensile strength and seam slippage are expected to sit inside the textiles delegated act. I want to be careful with the timing, because this is where the industry gets sloppy. The regulation itself came into full application on 19 July 2026. The textiles delegated act carries an indicative adoption target of 2027, and a delegated act cannot apply earlier than eighteen months after entering into force, which puts realistic mandatory compliance at 2028 or later. Adoption, entry into force and application are three different dates and collapsing them into one is how a supplier ends up promising something nobody has legislated.
The commercial pressure is arriving faster than the legal one in any case. Durability now sits in the top four purchase drivers for 62 per cent of shoppers. That is a large enough number that the first supplier to publish real figures will make life difficult for everyone still saying hard-wearing.
What I would ask before signing a uniform contract
Three questions, and write down the answers. Was the test run on the fabric or on the finished garment, and if only the fabric, what do you know about the seams? Was it run before or after washing, and how many washes? And can I see the report itself rather than a summary sheet? We attach lab reports to the production lot they came from, so a school can pull up the evidence for the batch its own children are wearing rather than a generic document about a fabric that may or may not be the one in the box.
As for the honest answer to the original question: a well-made blazer should comfortably outlive the child's size, which is usually eighteen months to two years. Beyond that, wear is rarely what ends it. Growth is, and that is a different problem entirely.