Ask ten suppliers for the gsm of a pad and you will get ten confident numbers. Almost none of them can be checked on the product you receive. Gsm is a property of a roll of material measured on a fixed area, and a finished pad is a laminated, embossed, folded stack of four or five different rolls. The figure survives the purchase order and dies at the packing line. That is not a trick; it is a unit mismatch, and it costs buyers real money.
What a gsm number actually describes
Gsm is grams per square metre. On a nonwoven line it is measured by punching a disc of known area out of the web and weighing it on a balance. The cutter fixes the area, so the only variable left is mass. That is why the figure repeats reliably inside a laboratory and tells you much less once the material has been bonded into a product.
The measurement also has a location, which is usually left out. A roll is wider than the pad cut from it, and fibre distribution across the width is not flat. Edges tend to run lighter than the centre because the web is formed and then drafted. A supplier reporting one figure is reporting an average, and an average hides the strip your die actually uses.
Why a finished pad never carries one figure
A pad is not a sheet. It is a top layer, an acquisition layer, a core, a backsheet, and often a second core layer, bonded and then embossed. Each layer has its own area density, and the core is usually built as a gradient so liquid moves away from the surface faster than it arrives.
Embossing changes local density again. The pattern compresses the stack at the bond points and leaves the fields between them loose, so two pads from the same laminate can differ in thickness at identical total mass. When a purchase order names a single figure for the finished product, the plant that runs the laminate has to guess which layer was meant, and the guess it picks will be the cheapest one.
Where a sanitary pad gsm specification belongs
A sanitary pad gsm specification belongs on the incoming material sheet, not on the finished product sheet. That single move settles most arguments that begin with the words your pads feel thinner. The material sheet is checkable: you can cut, weigh and reject a roll at the goods-in bay, before anything is laminated.
The finished product has its own checkable properties, and none of them is area density. Thickness under a defined load, liquid absorbency, rewet and strike-through are all measurable on the pad itself. Ask for those in the product spec and keep the material spec separate. Buyers who merge the two documents end up with one figure that nobody can verify.
How absorbency is reported, and why it travels badly
There is no single sanitary pad absorbency test method. There are several families of method and they answer different questions. One soaks a sample freely and weighs the gain. Another applies a load during the soak, which stands in for a body resting on the product. A third drips liquid at a set rate and records when uptake stops.
The same pad can look strong under one and weak under another. A free soak reports capacity. A loaded soak reports usable capacity, and the gap between the two is the liquid that the pad holds but gives back under pressure. Neither number is wrong; they answer different questions, which is why a figure quoted without its method is not evidence of performance.
Published nonwoven test methods carry a condition line for this reason: specimen area, load during the test, soak duration, and the point on the product the sample came from. A laboratory that leaves the condition line out is not being secretive. It is reporting a number that cannot be compared with anyone else's, including its own from last year. The bench we run records the same four items, and the habit came from being asked to explain a number twice.
Rewet numbers follow the applied load
A sanitary pad rewet test measures how much liquid returns to a stack of filter paper pressed against the surface after the pad has taken a dose. Everything that decides the result sits in the setup: the weight placed on top, the number of filter papers, how long the load stays, and how long after the dose the reading is taken.
Change the weight and you can reverse the ranking of two pads. A core that holds liquid loosely will pass a light load and fail a heavier one, because the same liquid is simply easier to press out. This is why rewet figures from two suppliers so often contradict each other, and why comparing two rewet numbers without comparing their loads compares nothing at all.
Filter paper is the other quiet variable. More sheets absorb more of what comes back, so a thicker stack reports a lower figure on the same pad. Serious reports state the stack, the load and the interval. If a data sheet gives a rewet value and none of those three, the value describes the laboratory rather than the product.
Strike-through time on the second and third insult
Sanitary pad strike through time is the interval between liquid landing on the surface and disappearing into the core. On the first dose almost every product looks fast, because the top layer is dry and the acquisition layer is empty. The number worth asking for is the third dose, or the fifth.
By then the acquisition layer is partly filled and the core below is no longer pulling hard. A thin core shows up here first, long before total capacity becomes the issue. The pad still holds what it was designed to hold; it just takes longer to move each later dose away from the surface, and the wearer experiences wetness rather than a visible failure.
This is the failure mode an area density figure cannot predict. Lowering density in the core reduces cost and also reduces the capillary pull that drives liquid downward, so the first symptom is a longer third-dose time and a higher rewet under load, not an overflowing pad. Buyers who test only capacity will never see it coming.
Writing a spec that someone else can check
Four parts make a sanitary pad gsm specification workable, and a single number has none of them: a target, a tolerance band, a named method, and a sampling position. Add the document each one lives on, and the argument about thin pads stops being a matter of opinion.
| Item | What to state | How it gets checked |
|---|---|---|
| Top layer | Target with a tolerance band | Disc cut from the roll, weighed |
| Core | Target plus gradient direction | Sectioned sample, each zone weighed |
| Backsheet | Target plus thickness under load | Disc cut, weighed, then gauged |
| Finished pad | Thickness, absorbency, rewet, strike-through | Tested on the pad, method named |
Gradient direction matters as much as the figure. A core built heavier at the bottom and lighter at the top moves liquid away from the skin; the reverse does the opposite at the same total mass. Two rolls can weigh the same and behave in opposite ways, which is one more reason a single figure cannot describe a stack of layers.
State the sampling position once and apply it to every shipment. Centre of the web, edge of the web, or a composite of both are all defensible choices; mixing them between shipments is not. When a roll arrives short of the figure, the first question will be where the disc came from, and the answer needs to be in the document already. The questions we get most often about this are almost always about which document, not which number.
Settle these before you accept a tolerance band
Tolerance is where most disputes actually live. A band that is tight on paper and loose in practice is worse than an honest wide band, because it invites rejection on the first container and argument on the second. Ask what the line can hold across a full run, not what it can hold on a hand sample.
Ask too which layer the band applies to, and whether the figure is measured before or after lamination. Bonding and embossing shift local density, so a roll that passes at goods in can produce a pad that reads differently at the end of the line. Both readings can be true, and a spec that does not say which one it means will be argued about twice.
The tolerance inside a sanitary pad gsm specification also has a price. Holding a narrow band means slower line speed and more rejected web, so the band is a commercial choice before it is a technical one. It is worth setting it against the order size you will actually place rather than the sample you approved. A MOQ conversation usually settles that faster than a technical one.
We build pads and pants in Guangdong and have done so since 1998. The specification arguments that reach us are rarely about the number itself; they are about which document the number belongs on and who will check it. If you are rewriting a material sheet now, tell us the layers you buy and the tolerance you can live with, and we will send the measurement method alongside the target.
Frequently Asked Questions
Is gsm the same as pad thickness?
No. Gsm is mass per unit area and thickness is a distance, so a looser stack can be thicker at the same mass. Thickness has to be measured under a stated load to mean anything, which is why the two figures can move in opposite directions on two pads that weigh the same.
Which document should carry the gsm figure?
The incoming material sheet. Area density is measurable on a roll and not on a bonded, embossed product, so putting it on the product sheet creates a promise nobody can test. Keep absorbency, rewet and strike-through on the product sheet instead, and name the method next to each one.
Why do two suppliers report different rewet values?
Because the load, the number of filter papers and the reading interval are probably different. A heavier load presses more liquid back out and a thicker paper stack absorbs more of it, so the setup can move the figure further than the product does.
Can a pad pass capacity and still feel wet?
Yes. Capacity describes how much the core can hold, while strike-through time and rewet describe how fast liquid leaves the surface and how much returns under pressure. A pad can hold its rated volume and still feel wet on the third dose if the core pulls weakly.
What should a buyer ask for instead of a single figure?
A target with a tolerance band, the method used, the sampling position, and the document the figure lives on. Ask also for the load and the interval behind any absorbency or rewet value, since a figure without its conditions cannot be compared with another supplier.
