pH testing measures the acidity or alkalinity of a water extract of the fabric, and for textiles worn next to the skin the result is usually required within about 4.0 to 7.5. The test exists because dyeing, bleaching and finishing use strong alkalis and acids, and a fabric that has not been neutralised and rinsed properly carries that residue into the garment.
Skin is mildly acidic, and a fabric that is strongly alkaline or acidic can cause irritation, particularly for babies and people with sensitive skin. pH also affects colourfastness, since residual alkali can keep shifting a reactive dye after the fabric leaves the mill. It is one of the cheapest tests on the list and one of the most frequently failed.
How the test works
The lab cuts the fabric into small pieces, shakes it in distilled water for a set period, and measures the pH of the extract with a meter. It is a quick, inexpensive test, often included in the standard pre-shipment package. The result is a single number with no grades, which makes it easy to specify.
Because the test uses a water extract, it reflects what sits on the fibre surface and what a wearer's sweat would dissolve. It does not depend on the fibre type, so it is applied to cotton, viscose, polyester and blends alike. Read it alongside the colourfastness results, since a high pH on reactive-dyed cotton often explains a poor washing or perspiration fastness grade on the same fabric.
Why Indian fabrics fail pH
- Reactive dyeing on cotton uses soda ash, and an inadequate final rinse leaves the fabric alkaline.
- Mercerisation and scouring use caustic soda that must be fully neutralised.
- Some finishing baths are acidic and are applied without a final wash.
- Water and effluent costs encourage short rinse cycles when the mill is under pressure.
Specifying and interpreting pH
Put the pH range in the purchase specification rather than relying on the lab's default. OEKO-TEX and most brand restricted substances lists set ranges by product class, and babywear is the strictest. A fail is usually easy to correct with an additional neutralising rinse, so a pH problem caught on a bulk sample before loading rarely costs the shipment, whereas one found in the destination market does. For a first order with a new mill, test pH on the first bulk lot rather than waiting for the full quantity, so a rinsing problem shows up while there is still time to correct the process.
Requirements change and differ between buyers, so confirm the range with an accredited lab or your compliance team. This is general information, not legal advice.
How we handle pH
We put the pH range for your market into the test plan, draw sealed samples from the bulk and send them to an NABL-accredited or international lab. If the result is out of range we go back to the mill for a further rinse and retest before anything is loaded, then supervise the loading. You get a weekly update, and a free 20-minute sourcing review if you want to set up a test plan for a new supplier.