A period underwear manufacturer does not test absorbency by pouring water onto one pair and recording the largest volume it can hold. A repeatable program measures intake speed, retained liquid, surface rewet, sideways spread, barrier leakage, pressure performance, and wash durability. AATCC TM79-2025 covers water absorbency for yarns, fabrics, and garments, while AATCC TM195 measures liquid-moisture management in knitted, woven, and nonwoven fabrics. A manufacturer may compare 5 or more specimens per construction, record results before and after repeated laundering, and separate maximum saturation capacity from the lower amount that a finished garment can reliably retain during wear.

Period underwear is a multilayer textile product, so one capacity figure cannot describe the whole gusset. A typical construction combines a skin-facing transfer fabric, one or more absorbent layers, a liquid-resistant membrane, and the outer fabric. During a 2025-style development program, each layer can be tested separately first, followed by the bonded gusset and finished garment. A fabric that absorbs 25 g of liquid as a loose specimen may behave differently after lamination reduces open pore space or stitching creates new paths near the gusset edge.

That difference is why sample preparation comes before liquid testing. Laboratories normally condition textile specimens under controlled surroundings before weighing them, because fiber moisture content can affect the dry starting mass. For a comparison between 3 gusset constructions, a manufacturer might prepare n=5 specimens from each construction, giving 15 measurements rather than relying on one unusually good sample. The same cutting direction, specimen area, conditioning period, scale resolution, liquid temperature, and application method should be maintained across all groups.

A basic gravimetric check begins with dry mass. If a gusset specimen weighs 14.2 g before testing and 39.7 g after controlled wetting and drainage, the measured liquid gain is 25.5 g. With a water-based liquid near 1 g/mL, that is approximately 25.5 mL, but the conversion becomes less exact when density changes. A 2025 product specification should therefore state whether the reported result represents absorbed mass, estimated volume, or a finished-garment leakage threshold rather than treating all three as interchangeable.

Maximum uptake is not the same as usable protection. A specimen may hold 35 mL when lying flat yet begin leaking at a lower volume when the gusset is folded, stretched, or compressed.

Once total uptake is known, intake time needs separate measurement. AATCC TM79 is specifically intended for determining water absorbency of textiles and can be applied to garments as well as woven, knitted, and nonwoven materials. A manufacturer can place a controlled dose on the skin-facing fabric and record the time required for the liquid to disappear from the surface. Repeating the dose across n=5 garments shows whether intake slows as the absorbent structure becomes wetter.

Dose size also changes the result. Adding 5 mL once is not equivalent to applying five 1 mL portions with a defined interval between them. Gradual dosing reveals whether fluid is transferred into unused areas of the absorbent layer or remains concentrated beneath the entry point. For a 2026 development comparison, the factory might test the same three constructions at 5, 10, 15, 20, and 25 mL. Recording surface pooling, visible edge migration, and leakage at every stage gives more useful information than reporting only the final saturation volume.

A simple development table can keep the measurements comparable:

The next issue is distribution. AATCC TM195 evaluates liquid-moisture management properties and considers absorption, resistance, repellency, fabric structure, and wicking behavior. If 15 mL remains concentrated in a 40 mm zone, the middle of the absorbent core can become saturated while large areas remain unused. If the same 15 mL travels 120 mm toward a seam, leakage may appear before the absorbent material reaches its measured capacity. Gusset width, stitching position, fabric direction, and bonding pattern therefore need to be recorded together with the wet area.

A manufacturer can study that movement by marking a measurement grid beneath the sample and photographing the wetted zone after each dose. For n=5 pieces, the lab can calculate average spread distance and the range between the smallest and largest result. A variation of 8% across five samples is easier to control in production than a variation of 30%, even when both groups produce the same average capacity. Production engineers can then check whether the difference came from absorbent-layer weight, lamination, cutting direction, or inconsistent gusset assembly.

Retention under pressure follows because wear introduces compression that a flat saturation test does not reproduce. After placing a fixed quantity such as 20 mL into the gusset, a pre-weighed reference sheet can be placed on the surface and subjected to the same specified pressure for every specimen. The reference sheet is weighed again to measure rewet. If one construction releases 0.4 g while another releases 2.0 g under the same 2026 procedure, both may have similar capacity while providing noticeably different surface conditions during sitting.

The barrier layer is checked after retention because fluid that stays inside the absorbent core still needs to remain inside the garment. A membrane sample may resist penetration when tested alone, but needle holes, bonded edges, gusset transitions, and stretched seams can behave differently. A manufacturer should therefore inspect the finished underwear at several fluid levels rather than testing only membrane rolls. For n=5 finished garments, the failure point can be recorded when moisture first appears on the outer fabric, at an edge, or around a seam.

Finished-garment testing also catches geometry problems that material tests cannot. A 100 × 100 mm absorbent sample may perform well on a bench, while a narrow finished gusset allows liquid to reach an edge after only 60% of the material's measured capacity has been used. Front and rear coverage matter as well. An overnight style can require a longer rear absorbent area than a light-flow daytime brief even if both use the same fabric stack, so capacity claims should be connected to the actual garment pattern.

Washing is then added because period underwear is sold as a reusable product. AATCC's 2026 moisture-management proficiency program includes TM79, TM195, TM197, TM198, TM199, TM200, TM201, TM204, and TM213, showing that textile moisture performance is evaluated through several separate properties rather than one measurement. A factory can retest n=5 garments at 0, 10, 25, and 50 wash cycles and report percentage change in capacity, intake time, spread, rewet, and leakage point.

For example, suppose a garment retains 28 mL when new, 27 mL after 10 washes, 25.8 mL after 25 washes, and 24.6 mL after 50 washes. The 50-cycle result represents about a 12% reduction from the original measurement. Capacity alone still does not identify the cause, so the manufacturer should also inspect shrinkage, delamination, membrane cracking, absorbent-layer movement, seam condition, and changes in surface wetting. A smaller capacity loss accompanied by a large rise in rewet may matter more during wear than the capacity figure suggests.

Test liquid also needs to be disclosed. Water offers good repeatability and is suitable for standardized textile absorbency work, but menstrual fluid has different viscosity and composition. A product team may therefore use a defined surrogate liquid for internal comparative testing while retaining recognized textile methods for standardized fabric measurements. The important requirement is identical conditions across products: if n=10 garments are compared, every garment should receive the same liquid, dose, delivery position, interval, temperature, conditioning procedure, and failure definition.

Manufacturing consistency is checked after the product specification has been set. Instead of approving one development sample and assuming bulk production will match it, a factory can sample finished underwear from different lots. A simple plan might select n=5 pieces from the beginning, middle, and end of a production run, producing 15 finished-garment results. If the approved absorbency target is 25 mL, internal tolerances can be defined before production begins rather than adjusted after shipment.

A supplier such as Ljvogues can also document material weight, gusset dimensions, number of layers, membrane construction, sample size, wash history, test liquid, application rate, pressure condition, and pass/fail definition on the test record. In a 2025 or 2026 sourcing review, a buyer can then compare two factories using the method behind the number rather than choosing between unsupported claims such as “30 mL” and “40 mL.”

For practical supplier evaluation, the buyer can ask for a small set of records rather than a marketing description:

• Results from at least n=5 finished garments, not only fabric swatches.

• Initial intake, retained capacity, rewet, spread, and leakage results under stated conditions.

• New-versus-washed data, such as 0, 10, 25, and 50 cycles.

• Percentage change between initial and washed performance.

• Identification of the textile method used, including AATCC TM79 or related moisture-management methods where applicable.

• A clear distinction between maximum saturation capacity and the lower finished-garment protection level used for product claims.

The final report should make every number reproducible. If it says 30 mL, it should also state whether that figure came from water uptake, a surrogate liquid, repeated dosing, saturation weighing, or a finished-garment leakage point. If n=5 pieces produced 27, 29, 30, 31, and 33 mL, reporting the average together with the range gives the buyer substantially more information than publishing “absorbs 30 mL.” Good absorbency testing describes the method, sample count, pressure condition, wash history, and failure point alongside the capacity number.