Buyers argue about hydrostatic head more than about any other figure in Oxford, and they usually argue about the wrong part of it: the number itself rather than the tolerance behind it.
What hydrostatic head actually controls in Oxford
Water resistance. 800 mm is shower-proof, 3000 mm handles sustained rain.
It also explains why hydrostatic head is the first line a buyer loosens and the last line a claim refers to.
For Oxford fabric, the working range is 800-5000 mm. Inside that band the choice is commercial; outside it, the product changes category and so does the price.
What 800-5000 mm does not tell you
| Position | Value | Effect on Oxford | Where it shows up |
|---|---|---|---|
| Floor | 800 | Lowest cost, least margin for process variation | Shade variation between lots within a season |
| Working middle | 800-5000 mm | Predictable performance at a normal price | Nothing to negotiate, nothing to explain |
| Ceiling | 5000 mm | Best performance, highest cost | Cost the end product may not recover |
Buyers default to the floor because it is the cheapest compliant answer. That is rational until the first claim, and then the saving is measured against a replacement shipment.
The figure that decides the outcome is not hydrostatic head itself but the tolerance around it. A supplier who quotes 800-5000 mm without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.
How to measure hydrostatic head
The reference method here is Coating adhesion, run to ISO 2411, with an acceptance of >= 6 N/50 mm. The method is the easy part; sampling and conditioning are where reports diverge.
Take samples from the beginning, middle and end of the run. A single sample from the top of a roll tells you about the top of that roll, and hydrostatic head varies more across a run than most buyers expect.
Record the measured value rather than pass or fail. A marginal pass on hydrostatic head tells you the process is running at the edge, which is the information you need before the next lot rather than after it.
Hydrostatic head does not stand alone
Hydrostatic head moves with base weight (90-260 gsm before coating) and with tear strength (>= 25 N warp / >= 25 N weft (600D)). Tightening one usually costs money in another, and a supplier who accepts every tolerance without comment has either not understood the interaction or is planning to substitute.
This is why a specification written as a list of independent tolerances is weaker than one written as a construction. The list lets a supplier satisfy each line while missing the product.
The clause to write for hydrostatic head
The line below is the version we can quote against without inventing anything. Hydrostatic head appears with a tolerance and a test, not as a standalone number.
600D polyester oxford, 2-pass PU coating with primer, 1500 mm hydrostatic head, 155 cm usable, 62 gsm total coating, tear >= 25 N, Pantone 19-4052 TCX, hydrolysis-resistant
The clause that protects you is not the value, it is the sentence that says what happens when the value is missed. Put it in the purchase order, not only in the enquiry.
When hydrostatic head goes wrong
Shade variation between lots. Panels cut from two deliveries read as different colours on the same bag.
The cause is usually dye lot change without a light-source check.
The test that catches it: Visual assessment under D65 and TL84, plus spectrophotometer dE <= 1.0.
What to specify instead: Ask for lot segregation and a retained standard; never mix lots in one production run.
Note that the fix is a specification change, not a negotiation. By the time the claim is made, the only remaining lever is who pays for it.
Four questions about hydrostatic head, before you order
- What tolerance do you hold on hydrostatic head, and what did your last three lots measure against it?
- Which method do you use for coating adhesion, and which laboratory signs the report?
- When hydrostatic head falls outside 800-5000 mm, do you rework, downgrade, or ship and hope?
- Which of base weight or tear strength would you move first to hit a lower price?
The answers are more useful than a certificate, because they show whether the process is controlled or merely inspected. Full ranges for Oxford are on the product page, and the measurement regime is described on the quality control page.
Questions buyers ask before ordering
Do you supply seam tape?
Yes, and we recommend testing the sewn sample rather than flat goods, because most leakage claims come from needle holes.
Is 600D always stronger than 420D?
Only if the yarn is genuinely 600D and the weave is tight. Cheap 600D with loose picks tears below a good 420D. Ask for the tear test, not the denier figure.
Three questions, and the answers that separate mills
If the Oxford figures on this page is going to be decided on a call, take these three questions into it.
| Question | Answer that should worry you | Answer that holds up |
|---|---|---|
| Which test catches coating peeling? | “We have never had a complaint.” | Tear strength — on the production lot, with the acceptance figure written into the report and not into the email. |
| May I see a report for a lot you shipped last month? | “That is confidential customer information.” | A redacted report, which carries every number that matters and none of the customer’s identity. |
| Where in the 90-260 gsm before coating band will this order sit? | “In the middle, normally.” | A stated target and the readings behind it. Base weight drifting inside the band is how a conforming lot still fails. |
Failure modes, and the test that catches each one
A specification only earns its keep if it names the failure it prevents. These are the two that matter for the Oxford figures on this page.
| Failure | What triggers it | Test to demand on the production lot |
|---|---|---|
| Shade variation between lots | Dye lot change without a light-source check. | Tensile strength — ASTM D5034 grab; acceptance >= 400 N warp for 600D |
| Coating peeling | Under-cured coating, too heavy a single pass, or no primer on the base fabric. | Coating adhesion — ISO 2411; acceptance >= 6 N/50 mm |
The other two, with acceptance numbers attached, are in the full failure analysis for Oxford. A supplier who cannot name the mode he sees most often is describing a catalogue, not a process.
Need hydrostatic head specified and tested against your end use?
Send the end use, the quantity and the destination market, and we will come back with a specification that meets it, a price at your volume and the test reports that back it up. Samples are free for qualified programmes; we charge the courier only.
Related reading
Sample cut with your values on it · Neutral packing and private label · Consolidation, documents and lead times
