When you change a soft diaper for your baby with infinite love, you may never have thought about what makes up this small pad that comes into intimate contact with your baby’s most delicate skin every day? What brings a baby a peaceful night’s sleep without any leakage?
I guess the first reaction of many novice parents is’ cotton ‘. After all, cotton gives the impression of being soft, natural, and absorbent. However, the fact may surprise you – the core mystery of the high-end diapers you use for your baby every day is not natural cotton, but a substance that sounds incredibly industrialized: polypropylene (PP), which is the most common plastic raw material in the non-woven fabric field.
Do you remember the ‘behind the scenes hero’ we discussed in our previous article? That’s right, it’s it again, PP non-woven fabric. Masks, wet wipes, diapers, these seemingly unrelated disposable hygiene products ultimately all point to the same core material. This is not a coincidence.
In the mask, PP non-woven fabric is responsible for filtering viruses; In wet wipes, it ensures moisture and strength; In the extremely complex multi-layer “liquid suction control system” of diapers, PP non-woven fabric plays two crucial but completely different roles - flow guiding layer and bottom film .
Does this sound a bit unbelievable? In diapers, materials from the same family need to quickly absorb liquids (hydrophilic) while firmly blocking liquid leakage (water repellent); It should not only have a fluffy and soft contact with the skin, but also be tough, reliable, leak proof, and breathable. Today, let’s dismantle it all at once: Why is it necessary to use PP in the flow guide layer and bottom film of diapers?
Diversion layer: a clever yet crucial “drainage conduit”
The structure of a piece of diaper is much more complex than we imagine. It is usually divided into four layers from top to bottom: the skin friendly surface layer that comes into intimate contact with the baby’s skin, the flow guiding layer that quickly spreads urine, the absorbent core layer that absorbs and locks in liquid (composed of fluff pulp and high water absorbent resin SAP), and the outermost impermeable bottom layer.
Among them, the diversion layer is extremely low-key, located below the surface layer and above the core layer, but can be regarded as the “nerve center” of the entire system. When a baby urinates, the liquid does not penetrate vertically downwards, but is quickly directed towards the surrounding area in the first layer, ensuring that the absorbent core of the entire diaper is evenly utilized, rather than being “unevenly drained” – the front area is already saturated and leaking, while the back area is completely dry.
The ability of PP non woven fabric here is precisely due to its strong plasticity. Manufacturers will mix PP fibers with ES (polyethylene/polypropylene two-component) fibers and use hot air nonwoven technology to make a flow guiding layer. This process enables the flow guiding layer to achieve an ideal fluffy structure – the flow guiding layer can temporarily store more than 10 times its own mass of liquid and has excellent resistance to backflow. When the liquid passes through the surface layer and reaches the guiding layer, the fluffy fiber mesh will quickly capture it, and after temporary storage, it will immediately spread to the periphery until it is completely absorbed by the core layer below.
But PP is naturally a ‘hydrophobic material’, with no hydrophilic groups on its surface, making it difficult to absorb water. To make it work in the diversion layer, it is necessary to undergo hydrophilic post-treatment. By adding 1% to 1.5% hydrophilic finishing agents, researchers can make PP non-woven fabrics possess both hydrophilic and soft properties. The processed PP flow guide layer can quickly guide liquid infiltration without allowing the liquid to flow back and irritate the baby’s skin.
Bottom film: the “ultimate trump card” for waterproof and breathable diapers
If the diversion layer solves the problem of “where does the liquid go”, then the bottom membrane (also known as the anti-seepage bottom layer) solves the problem of “where does the liquid stop” – its responsibility is to firmly seal the huge amount of urine locked by hundreds of millions of water absorbing particles inside the diaper, so that not a single drop leaks outside.
The design of the bottom film is truly exquisite. The bottom film of modern high-end diapers is not simply a layer of plastic film, but a set of double-layer composite structure : the inner layer is PE or PP microporous breathable film , which undertakes absolute waterproof and barrier responsibilities; The outer layer is compounded with a layer of PP spunbond non-woven fabric, which provides a soft touch, supports printing brand patterns, and enhances overall comfort.
That layer of microporous breathable membrane is a milestone invention in the field of disposable healthcare for humanity. Manufacturers will use PP or PE as a carrier, add about 50% calcium carbonate filler to the material, extrude it into a film, and then perform directional stretching. During stretching, interface delamination occurs between calcium carbonate particles and polymers, forming a large number of curved pore channels at the nanometer or micrometer level.
The magic of this film lies in its small pore size, winding channels, and the surface tension of the liquid that prevents water molecules from passing through (waterproofing); And the size of water vapor molecules is much smaller than the pore size, allowing them to freely pass through (breathable). In other words, the bottom film of diapers can prevent urine leakage while timely expelling the hot and humid inside, avoiding the baby’s buttocks from being in a warm and humid environment for a long time. Medical research shows that when the local temperature of the skin exceeds 34 ℃ and the humidity exceeds 80%, it significantly increases the risk of microecological imbalance in the diaper area.
This is also why many mothers are confused – ‘Even though the baby’s diaper is not wet, why does it feel damp when touched outside?’ In fact, this layer of moisture is proof of the breathable membrane’s work: the moisture is successfully expelled, rather than being trapped inside and damaging the baby’s skin. If the breathability is poor, it may actually lead to allergic reactions such as eczema on the baby’s skin.
How PP non-woven fabric truly achieves “skin friendly without irritation”
Now, let’s return to the question that many parents are concerned about: after all, PP is plastic, is it really safe to come into contact with your baby’s most delicate skin?
The answer is: quite safe . Multiple third-party laboratory test results have confirmed that the PP non-woven fabric additive used for baby diapers has no irritation or sensitization to human skin, does not contain PFAS, and is not on the EU ECHA’s “Substances of Very High Concern” list. It can even be used for food contact grade applications. At the same time, professional disposable hygiene products undergo skin allergy testing, which checks every layer from raw materials to finished products to ensure that diapers do not cause excessive irritation to the skin during use.
While the material is skin friendly, the texture is also constantly evolving. By adding only 0.5% ultra soft masterbatch, the softness of PP non-woven fabric can be significantly improved, and the texture of the fiber surface becomes smooth and skin friendly, without relying on traditional plasticizers or other chemical softeners.
You should know that the stratum corneum of newborns is only one-third as thick as adults, and the skin barrier is extremely fragile, extremely sensitive to friction, heat, and chemical stimulation. The reason why global diaper manufacturers unanimously choose PP non-woven fabric as the core material for the flow guiding layer and bottom film is precisely because it achieves an irreplaceable balance between safety, breathability, skin friendliness, and cost-effectiveness.
Write at the end
Of course, like many disposable hygiene products, PP non-woven fabric also faces challenges in terms of biodegradability and environmental protection. With the continuous improvement of consumers’ environmental awareness, biodegradable polylactic acid (PLA) non-woven fabrics have emerged as the future development direction of the industry. But at least for now, PP non-woven fabric still firmly occupies an irreplaceable position with its comprehensive advantages in cost, performance, and safety.
Have you gained a deeper understanding of the functions of the flow guiding layer and bottom film in diapers used by babies? Next time you choose diapers for your baby, you may want to pay more attention to the ingredient instructions. Products that can proactively label “breathable bottom film” and “high-efficiency flow guiding layer” often imply the brand’s solid foundation and pursuit in PP non-woven fabric application.
After all, the deeper we delve into peeling a small piece of diaper, the more we can discover that industrial civilization’s relentless pursuit of softness, dryness, and peace of mind is far more complex than you might imagine.
Dongguan Liansheng Non woven Technology Co., Ltd. was established in May 2020. It is a large-scale non-woven fabric production enterprise integrating research and development, production, and sales. It can produce various colors of PP spunbond non-woven fabrics with a width of less than 3.2 meters from 9 grams to 300 grams.
Post time: Jun-13-2026