A period underwear manufacturer develops leakproof products by controlling how liquid moves through several fabric layers rather than relying on one waterproof sheet. A typical gusset uses 3–5 layers: a skin-contact layer for fast transfer, an absorbent layer for storage, a barrier membrane, and sometimes a stabilizing or outer layer. Development teams measure absorption in milliliters, liquid transfer time, wet-back under pressure, seam leakage, dimensional change, and performance after repeated washing. ISO 811:2018 provides a recognized method for water-penetration resistance, while ISO 6330:2021 provides standardized domestic laundering procedures. A 20–40 mL capacity claim is useful only when the garment can retain that liquid under movement and pressure.

The first development work normally starts with a product specification rather than fabric purchasing. A manufacturer needs to define whether the underwear is intended for light daytime flow, moderate flow, heavier use, overnight wear, or backup protection with another menstrual product. A light-flow brief may target roughly 10–15 mL of usable absorption, while higher-capacity products may be developed around 25–40 mL or more. Those numbers are product targets, not universal industry grades, so the same “heavy” label can describe different capacities across brands.

Capacity alone does not describe how the underwear behaves on a person. Menstrual fluid arrives over time, body position changes, and pressure rises while sitting, cycling, sleeping, or exercising. For that reason, product developers often separate several measurements instead of reporting only total absorption:

Once the target is defined, attention moves to the top layer because poor intake performance can make a high-capacity product leak before its absorbent material is full. Textile laboratories can use methods related to AATCC TM195 for liquid moisture management and AATCC TM197 or TM198 for directional wicking. A development batch may include 20–30 fabric specimens so differences between rolls, finishing conditions, and material directions can be seen rather than judged from a single swatch.

The skin-facing textile must move fluid away without feeling rough after repeated washing. Polyester-based technical knits can offer fast transfer and lower water retention at the surface, while cotton, viscose, modal, and other cellulosic blends may provide a softer hand but absorb more moisture into the fiber itself. Fiber content therefore does not tell the whole story. Yarn construction, knit density, finishing, pore size, and surface treatment can change liquid movement even when two fabrics show the same percentage composition on the label.

A fabric listed as 95% one fiber and 5% elastane can perform very differently from another fabric with the same composition if yarn size, knit structure, weight, finishing, and stretch recovery are different.

After liquid passes through the contact layer, the absorbent section has to spread and store it. Manufacturers may combine brushed polyester, microfiber, cotton-rich textiles, viscose blends, or other absorbent constructions. Using one very thick layer can increase bulk and drying time, so development often uses 2 thinner layers with different spreading characteristics. A 30 mL laboratory capacity is less useful when most of the liquid remains concentrated inside a 5 cm area instead of moving across the available gusset.

Spreading matters because menstrual flow is usually delivered to a relatively small contact area. If the first 5 mL remains near the center, local saturation may occur while much of the absorbent textile remains dry. Manufacturers therefore apply repeated doses at controlled intervals and observe lateral movement, surface wetness, and leakage. Testing may use 10, 20, and 30 mL loading levels to compare performance as the product approaches its intended capacity.

That absorbent construction then needs a barrier that stops liquid without turning the gusset into an uncomfortable plastic panel. Laminated polyurethane-based membranes are widely used in washable protective apparel because thin films can provide water resistance while retaining flexibility. ISO 811:2018 measures resistance to water penetration by hydrostatic pressure and remained a current ISO method after its 2025 review. A manufacturer can use this type of testing to compare membrane lots before assembling finished garments.

Membrane performance can change after lamination, sewing, stretching, detergent exposure, and heat, so raw-material results cannot replace finished-product checks. Needle holes are another concern. A membrane may resist water well as an unstitched sheet, while a seam crossing the protected area creates dozens of penetration points. For a stitch density near 4 stitches per centimeter, a 20 cm seam may contain roughly 80 needle entries, depending on stitch type and construction.

Manufacturers reduce that exposure through gusset shape, seam position, overlap width, stitch selection, and the way layers are secured. Some designs keep major seams outside the highest-flow zone; others extend the absorbent and barrier sections farther toward the front or rear. Overnight underwear often uses a much longer rear protection area because body position changes during 6–8 hours of sleep.

Fit testing follows because a technically good gusset can still leak when garment geometry creates gaps around the legs. A manufacturer may fit-test sizes on 15–30 wearers across several body measurements instead of approving a pattern from one fitting model. Waist circumference, hip circumference, rise, thigh opening, gusset width, and stretch recovery all affect how closely the protected section stays against the body.

• Leg openings need enough recovery to remain close during walking and sitting without excessive pressure.

• Gusset width must cover the intended area after the fabric stretches on the body.

• Front and rear rise influence where the absorbent panel sits during movement.

• Elastic recovery should be measured again after repeated laundering, not only on a new garment.

With construction established, washing becomes part of product development rather than an afterthought. ISO 6330:2021 defines domestic washing and drying procedures for textile testing and includes 16 washing procedures for Type A machines, 12 for Type B, and 7 for Type C, plus six drying procedures. Manufacturers can select an appropriate procedure and keep temperature, detergent, ballast, drying method, and cycle count consistent across samples.

A useful durability program checks garments at several stages rather than only after the final cycle. Measurements at 0, 10, 25, and 50 wash cycles can show when shrinkage, delamination, absorbency loss, elastic fatigue, or seam distortion begins. If a gusset shrinks 4% while the surrounding shell shrinks 1%, puckering may develop even when neither fabric fails individually. Matching dimensional behavior between layers is therefore part of leakproof engineering.

The same reasoning applies to chemical and material compliance. Underwear has prolonged skin contact, so brands serving Europe, North America, Australia, and other international markets commonly request restricted-substance documentation and third-party textile testing. OEKO-TEX STANDARD 100 is one recognized certification system for textiles tested for harmful substances, but certification scope has to match the actual material or finished article being sold. A certificate for one fabric does not automatically cover every component in a 4-layer finished garment.

Chemical requirements have also become more detailed since 2023–2026, especially around fluorinated substances in consumer textiles. Brands should therefore identify membrane chemistry, water-repellent treatments, adhesives, printing chemicals, elastic components, and finishing agents before production. Supplier declarations should be supported by appropriate third-party reports when required by the destination market rather than relying only on a material name such as “breathable membrane.”

For OEM and private-label development, communication between the brand and manufacturer affects how much of this work can be controlled. A supplier such as Ljvogues may receive requirements covering style, fabric composition, absorbency target, gusset dimensions, labeling, packaging, size range, and testing expectations. A more useful specification states “target retained capacity 25 mL after 50 wash cycles” rather than simply requesting “high absorbency.”

Production approval then moves from development samples to repeatability. A pilot run of 50–100 garments can reveal problems that do not appear in 3 hand-made prototypes: inconsistent lamination alignment, seam tension variation, flipped layers, adhesive contamination, or gusset placement differences between operators. Inspectors can cut selected garments apart after liquid testing to confirm that failures came from material performance rather than assembly errors.

Finished-goods sampling should include more than visual inspection. A practical control plan can combine measurements from several areas:

From a 500-piece production lot, selected garments can be checked for dimensions, seam condition, stretch recovery, liquid intake, retained capacity, and visible leakage under a defined load. The sampling level and acceptance criteria should be agreed before production because there is no single universal menstrual-underwear inspection rule covering every brand claim.

Absorbency claims also need consistent language. Comparing period underwear with “tampons” or “pads” can confuse shoppers because disposable products come in different regulated absorbency ranges and constructions. Reporting a tested capacity in milliliters gives buyers a measurable reference, but the method should state whether the figure represents saturation capacity, retained capacity after pressure, or a wearable-use target. A garment that absorbs 35 mL at saturation may have a lower practical capacity once compression and wet-back limits are applied.

Wear trials can then check issues that bench testing cannot fully reproduce. A manufacturer or brand may recruit 20–50 participants across different sizes and flow levels, recording wear duration, perceived dryness, shifting, side leakage, rear leakage, odor perception, washing behavior, and comfort. Feedback should be separated by size and intended flow level; mixing all responses into one average can mask a fit problem affecting only one size range.

Results from wear testing feed back into material and pattern revisions. Slow intake can require a different surface structure, concentrated saturation can require better lateral spreading, rear leakage can require a longer gusset, and repeated side leakage can point to width or leg-opening geometry rather than insufficient total absorbency. Development commonly requires 2–4 prototype rounds because changes to one layer can alter thickness, stretch, drying time, seam behavior, and fit elsewhere in the garment.

Before bulk production, the manufacturer can freeze a reference sample together with a bill of materials, fabric specifications, approved measurements, stitch requirements, testing method, wash conditions, packaging details, and acceptable tolerances. When later production uses the same material codes and construction settings, quality teams have measurable references for comparison rather than judging whether a garment merely “looks similar” to the original sample.