A UV card in every order

The shirt test

The shirt test shows whether sunlight gets through a shirt. Hold a UV card in the sun, then under one layer of the shirt, and compare the colour.

An illustration of the shirt test.

What the card shows

  • Illustration of a UV card on a white table in full sun, its sensor turned dark
    In the sun, the UV card changes colour in seconds.
  • Illustration of a UV card under one layer of a thin white shirt, its sensor turned partly dark
    Under one layer of a thin shirt, it very often changes colour too.
  • Illustration of two UV cards side by side on a white table: the one from the sun dark, the one from under a thin shirt partly dark
    Side by side, the two cards show how much of the sun got through.

Why a tight fabric matters

Sunlight passes through the small gaps between the yarns of a fabric. A loose, open knit lets more of it through than a tight one.

Every Rezzella fabric is knitted or woven tight, with no open mesh, so it is made to block the sun.

Sunlight passing through a loose knit, and stopped by a tight knitThe sun shines on two shirts that look alike. Magnified, the loose knit has open gaps between its yarns, so a few rays pass straight through it. The tight knit has no gaps, so every ray stops at the fabric.A loose knitA tight knit

What it shows, and what it does not

It shows

Whether sunlight gets through the shirt you are wearing, in the sun you are standing in. A UV card is printed with a substance that changes colour in ultraviolet light, and fades back out of the sun.1

It does not show

A lab rating. A card gives no number, and researchers found these indicators are of limited use for measuring how strong the sun is.1 The colour also depends on the temperature and on the mix of sunlight.2

Our lab test

Our fabric goes to ARPANSA, Australia’s radiation protection agency, for testing to AS/NZS 4399 before the first run. The full report goes on the shirt test page.

The full report will be published on this page after the lab test, with the laboratory, the standard, the date and the result. AS/NZS 4399 is the Australian and New Zealand standard for sun protective clothing.

Until the report is here, we say only this: made to block the sun.

A UV card in every order

The pieces

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Sources

  1. Aguilera J and others, Qualitative and quantitative analysis of colorimetric response in different UV solar radiation level indicator bracelets based on photochromic substances, Frontiers in Photobiology, 2024
  2. Weber M, Schulmeister K and Brusl H, Parameters influencing the accuracy and practical applicability of UV indicator cards, Photochemical & Photobiological Sciences, 2006

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