Cloth Diaper Inserts: Hemp vs Bamboo vs Microfiber Explained
The fiber inside your cloth diaper does more work than the cover, the snaps, or the stitching combined. Hemp holds the most moisture but absorbs slowly. Bamboo absorbs fast and feels soft against skin. Microfiber wicks the fastest of any material — but it should never touch your baby's skin. Understanding what each fiber actually does is the difference between a cloth setup that works and one that leaks.
Why Fiber Matters More Than Diaper Style
When parents have leaks or rash or capacity problems, the first instinct is usually to blame the diaper — the cover, the brand, the construction. But cloth diapers are simple objects: a waterproof outer, an absorbent inner, and elastic to hold them in place. The waterproof outer either keeps water in or it doesn't. The elastic either contains leaks at the legs or it doesn't. The variable that actually decides whether your cloth diaper performs is the absorbent layer — the insert — and what fiber it's made from.
Different fibers have different jobs. They absorb at different speeds. They release moisture under pressure differently. They hold different volumes. They feel different against skin. Picking the right fiber for the right situation — and combining fibers correctly when you need to — is the single highest-leverage decision in cloth diapering.
Insert vs Booster: The Difference and Why It Matters
Before talking about fibers, a quick vocabulary check that trips up most new cloth diaper parents.
The primary absorbent layer that goes inside a cover or pocket diaper. Inserts are designed to wick moisture quickly at the surface so baby doesn't feel wet, and to hold a reasonable volume underneath. Bamboo, rayon, and cotton are common insert fibers — fast at the surface, decent capacity, soft against skin.
A secondary absorbent pad that sits underneath an insert to add extra capacity. Boosters are typically smaller, denser, and made from higher-capacity fibers like hemp. They don't wick as fast as inserts, which is exactly why they go under the insert rather than on top — the fast-wicking insert catches the initial flood, the high-capacity booster below holds the overflow.
This distinction matters because using a booster as if it were an insert — putting it on top of a cover by itself — will leak. Not because the booster is bad, but because hemp absorbs slowly, and slow absorption at the surface means urine pools and escapes before it gets pulled in. The booster is a tool that only works as part of a stack.
Our Rayon Snap-In Inserts are inserts — they wick fast and work as the primary daytime layer. Our Hemp Cotton Booster Inserts are boosters — they hold the most volume, but they need to sit under another insert to perform correctly.
The Absorbency Ladder: How the Four Fibers Compare
This is the high-level comparison. The detailed sections below explain each fiber individually.
Hemp — Highest Capacity, Slowest Absorption
Hemp is the absorbency workhorse of cloth diapering. It holds significantly more moisture by weight than cotton, bamboo, or microfiber, and it holds that moisture deep in the fibers rather than at the surface — which means it doesn't squeeze back out under the pressure of a sleeping baby. This compression-leak resistance is why hemp is the standard choice for overnight cloth diapering.
The trade-off: hemp absorbs slowly. The fibers are dense, so it takes time for moisture to penetrate the surface and reach the inner layers where capacity lives. Used as a top layer by itself, hemp can let urine pool on the surface and escape before it gets absorbed. This is why hemp is almost always used as a booster — sitting under a faster-wicking insert that catches the initial flood and passes it down to the hemp underneath.
Overnight stretches. Heavy wetters. Long naps. Travel days. Anywhere the volume is high or the duration is long. Hemp is the only natural fiber that reliably holds 8 to 12 ounces overnight without compression leaks.
As a primary daytime insert. The slow surface absorption means quick changes can outrun what the hemp has had time to soak in. Hemp also takes 5–8 wash cycles to reach full absorbency — the fibers need to open up. First-night performance is not representative.
In practice, hemp is rarely sold as a primary insert at all — it's almost always sold as a booster, designed to sit underneath something else. Our Hemp Cotton Booster Inserts are 4 layers of 55% hemp / 45% cotton. The cotton blend speeds up absorption slightly while keeping the hemp's high holding capacity intact, and it makes the booster softer and easier to wash.
Bamboo and Rayon — Soft, Fast, the Daytime Default
Bamboo is the most common daytime insert fiber in modern cloth diapering, and for good reason. It absorbs quickly at the surface, holds a respectable volume, feels soft against skin, dries faster than hemp, and is naturally moisture-wicking and antibacterial. For a typical daytime change every 2 to 3 hours, a single bamboo or rayon insert is enough.
A note on terminology: most "bamboo" inserts on the market are technically rayon from bamboo (also called bamboo viscose). The bamboo plant goes through a chemical processing step that converts the cellulose into a soft, absorbent fiber — the result is technically rayon, but the source material is bamboo. True 100% bamboo fiber exists but is rare and stiff. When a cloth diaper is sold as "bamboo," it's almost always rayon from bamboo.
Daytime use, all day, every day. Newborns and young babies who need quick absorption to prevent rash. Babies with sensitive skin who can't tolerate microfiber. Anywhere you need a fiber that wicks fast, holds reasonably, and stays soft against skin.
Overnight stretches. Bamboo's holding capacity tops out below hemp's, and bamboo releases more moisture under pressure than hemp does. Used overnight on its own, a bamboo insert will compression-leak — which is why overnight setups use hemp as the booster.
Our Cloth Diaper Starter Kit includes bamboo inserts as the default daytime absorbent. For daytime users who want to scale up capacity or buy inserts independently of covers, our Rayon Snap-In Inserts are the daytime workhorse — three layers of rayon-from-bamboo, sized to fit baby through big kid diapers.
Cotton — The Workhorse Middle Ground
Cotton is the oldest cloth diaper material and still one of the most common, especially in prefolds, flats, and natural-fiber fitteds. It absorbs quickly, feels soft, and is gentle against skin — including newborn skin. Where cotton lands on the absorbency ladder is just below bamboo: similar absorption speed, slightly lower total capacity, slightly less compression-leak resistance.
Cotton's biggest advantage is durability. A well-made cotton prefold lasts for years through multiple children with minimal performance degradation, and prefolds are the cheapest cloth diaper option per absorbency unit on the market. The trade-off is bulk — cotton holds less per layer than bamboo or hemp, so achieving the same total capacity takes more material.
In modern two-piece systems, cotton is most commonly seen as the absorbent body of fitted diapers (often blended with hemp for added capacity), as the outer layer of hemp boosters (the cotton speeds up absorption while the hemp holds), and as the standalone fiber in prefolds and flats. Pure cotton inserts in cover systems are less common than bamboo or rayon equivalents.
Microfiber — Fast Wicking, Never Against Skin
Microfiber is the most common cloth diaper insert fiber on the budget end of the market — typically the fiber in cheap pocket diaper inserts and budget all-in-ones. It absorbs faster than any natural fiber, which is why it's used. But microfiber comes with two significant problems that natural fibers don't have.
Microfiber pulls moisture aggressively from anything it touches — including skin. On prolonged contact, it dries out the skin, can cause irritation and small cracks, and in some babies triggers persistent rash. This is why microfiber inserts in pocket diapers are designed to sit inside the pocket, with a wicking fabric layer between the microfiber and the baby — never directly against skin.
If you ever need to add microfiber capacity to a cover system (some heavy-wetter setups stack microfiber for fast initial wicking), it goes in the middle of the stack — under a natural-fiber insert that touches skin, on top of a hemp booster that holds.
Microfiber's structure holds moisture loosely — between the fiber strands, not deep inside them. Under pressure (a baby lying on a wet diaper, sitting in a car seat for an hour, sleeping for hours), microfiber releases that moisture back out. This is called compression leak, and it's why microfiber is a poor choice for overnight or long-stretch use.
The fix when you must use microfiber overnight is to layer it under hemp — the microfiber wicks the initial flood fast, and the hemp underneath holds it under pressure. But for most overnight setups, skipping microfiber entirely and using hemp under bamboo is the cleaner approach.
EcoAble does not include microfiber in our baby cloth diaper range — every absorbent in our system is hemp, organic cotton, bamboo, or rayon-from-bamboo. We mention microfiber here because it's a fiber you'll encounter in other brands' products, especially budget pocket diapers, and understanding its behavior helps you build a better cloth setup.
Charcoal Bamboo — The Marketing Fiber
"Charcoal bamboo" inserts have become popular on the budget end of cloth diapering, marketed as having superior absorbency and antibacterial properties because of activated charcoal. The honest assessment: charcoal bamboo inserts are usually microfiber inserts with a thin charcoal-bamboo layer fused to the surface. The bulk of the absorbency comes from the microfiber underneath; the charcoal layer is largely cosmetic.
This isn't necessarily bad — a charcoal bamboo insert in a pocket diaper does work, and the charcoal-bamboo top layer is more skin-safe than raw microfiber, so these inserts can sit closer to skin than pure microfiber inserts. But the marketed benefits — "naturally antibacterial," "superior absorbency" — are mostly attributable to the microfiber, not the charcoal.
If you encounter charcoal bamboo inserts, treat them as microfiber inserts with a softer top layer. Don't expect the absorbency profile of natural-fiber inserts. They're a budget option, not a premium one.
How to Layer Different Fibers Together
Cloth diaper systems perform best when fibers are layered to leverage each fiber's strength. The principle is simple: fast-wicking fibers go on top, high-capacity fibers go underneath.
Which Insert Should You Actually Buy?
The honest answer for most families: a bamboo or rayon insert for daytime, and a hemp booster for overnight and heavy-wetter situations. Two products cover almost every cloth diapering scenario.
If you're new to cloth, start with the Starter Kit and add hemp boosters once you've identified which situations (overnight, long naps, car rides) need extra capacity. If you're scaling an existing stash, the rayon inserts let you replace inserts independently of covers, and the hemp boosters slide into any system you already own.
Frequently Asked Questions
What's the best cloth diaper insert material?
It depends on the use case. For daytime, bamboo or rayon-from-bamboo is the best choice — fast absorption, soft against skin, good capacity. For overnight and heavy wetters, hemp (usually blended with cotton) is the best choice — highest capacity per layer and the only fiber that reliably resists compression leaks under a sleeping baby. Most families need both: bamboo or rayon as the daytime insert, hemp as the overnight booster.
What's the difference between an insert and a booster?
An insert is the primary absorbent layer that goes inside a cover or pocket — it wicks moisture quickly at the surface and holds a reasonable volume. A booster is a secondary absorbent pad that sits underneath an insert to add capacity. Boosters are typically smaller, denser, and made from higher-capacity fibers like hemp. They don't wick as fast as inserts, which is why they go underneath rather than on top.
Why can't I use a hemp insert by itself?
Hemp absorbs slowly. The fibers are dense, so it takes time for moisture to penetrate the surface and reach the inner layers where capacity lives. Used alone as the top layer, hemp lets urine pool on the surface and escape before it gets fully absorbed. Hemp's high capacity only matters if a faster-wicking fiber on top catches the initial flood and passes it down — which is why hemp inserts are sold as boosters, designed to sit under another absorbent layer.
Is microfiber bad for cloth diapers?
Microfiber isn't bad — it's just specialized. It absorbs faster than any natural fiber and is the most common insert fiber in budget pocket diapers. The two limitations: microfiber should never touch baby's skin (it pulls moisture aggressively and can cause dryness and irritation on prolonged contact), and microfiber compression-leaks under pressure (poor choice for overnight or long-stretch use). When microfiber is layered correctly — between an insert and a hemp booster — it works fine. EcoAble doesn't use microfiber in our baby diapers, but you'll encounter it in other brands.
Is bamboo or hemp better for overnight?
Hemp, by a meaningful margin. Bamboo is excellent for daytime but tops out at lower total capacity than hemp and releases more moisture under compression. Hemp holds significantly more per layer and holds it deep in the fibers, so it doesn't squeeze back out under the pressure of a sleeping baby. The standard overnight setup uses bamboo or natural cotton against the skin (in the fitted's lining) and hemp underneath as the booster — leveraging both fibers' strengths.
How many layers does an insert need?
For daytime use, 3 to 4 layers of bamboo or rayon is standard — enough capacity for a 2-to-3-hour change window without excessive bulk. For overnight boosters, 4 layers of hemp-cotton is the sweet spot — enough capacity to handle most overnight stretches when paired with a fitted, without the bulk that two stacked thinner boosters would create. More layers means more capacity but also slower drying time and more bulk; the goal is matching layer count to use case rather than always maximizing.
Do new cloth diaper inserts need to be washed before use?
Yes — and natural fibers (hemp, bamboo, cotton) need multiple washes to reach full absorbency. Hemp and cotton reach about 80% of their capacity by the third or fourth wash and full capacity around wash 5 to 8 as the natural oils flush out and the fibers open up. Synthetic fibers (microfiber, charcoal bamboo) reach full absorbency after one wash. The full prep routine for new cloth diapers is in our prep guide.
Can I use prefolds or flats instead of shaped inserts?
Yes — prefolds and flats are traditional cotton or hemp absorbents that work inside a cover or pinned with a fastener. They're typically the cheapest cloth option per absorbency unit, last for years, and are easy to wash. The trade-off is bulk and the learning curve for folding. Modern shaped inserts (like our Rayon Snap-In Inserts) are easier and faster to use, especially for caregivers unfamiliar with cloth, but prefolds and flats deliver the same absorbency for less money.