Choosing Period Underwear by Flow: A Practical Buying Guide

Quick answer

Match absorbency to your heaviest flow day, not your average one. For light days or backup, choose briefs that absorb around 15–20ml, like the Teens First Period Shortie. For heavy flow or overnight, choose a higher-capacity option such as the LBL Full Brief, which absorbs up to 40ml. If you are unsure, buy one pair in each range and test them on different days before committing to a full set.

Period underwear is not one product with one job. A brief that handles a light day will feel different from one built for a heavy flow, and buying the wrong absorbency is the most common reason people give up on reusables. The fix is simple: choose by flow first, then by fit and fabric.

This guide walks through the absorbency levels available in the Love Luna range, what the layer counts actually mean, and how to build a small set that covers your whole cycle without overspending on pairs you will never wear.

Start with your heaviest day, not your average day

Most people underestimate their flow because they compare it to a 'normal' day. Instead, think about your heaviest two days and buy for those. If you use a super tampon plus a pad on day two, you need a brief with a higher capacity, not a light pair. Buying for your heaviest day means you are covered when it matters and can still wear the same brief on lighter days with a longer wear time.

A practical test: track your flow for one cycle using a simple note on your phone. Mark heavy, medium, and light days. That pattern tells you how many high-capacity briefs you need versus lighter ones, and it stops you from buying a full set of briefs that only work for half your period.

• Count your heaviest days first; they set your minimum absorbency.
• If you leak through a pad in under two hours, size up in absorbency, not just in fit.

What absorbency levels actually mean in millilitres

Absorbency is measured in millilitres (ml), and the numbers are more useful than vague labels like 'light' or 'heavy'. A brief rated at 15–20ml is roughly equal to 3–4 regular tampons, which suits light flow, spotting, or backup on a heavy day. A brief rated up to 40ml is roughly 8 teaspoons, which suits moderate to heavy flow and overnight use.

The layer count is a separate spec from capacity. More layers usually mean more protection and a slightly thicker gusset, but the ml rating is the number that tells you how much fluid the brief can hold. Always check both: a 4-layer brief and a 5-layer brief can have very different capacities.

• 15–20ml: light flow, spotting, or backup.
• Up to 40ml: heavier flow, overnight, or long days without a change.

Match the brief style to your body and your day

Style affects comfort as much as absorbency. A bikini brief sits lower on the hip and suits lighter flow days or younger bodies. A midi brief offers more coverage through the seat and a flattering mid-rise fit. A full brief gives the most coverage and is often the better choice for heavy flow or overnight because there is more fabric to hold the absorbent layers in place.

If you are active, look for stretch. The Superstretch Period Midi Brief uses a stretch fabric designed to move with your body, which reduces bunching during sport or long walks. For swimming, a standard period brief will not work; you need swim-specific period swimwear with water-repellent fabric.

• Bikini: light days, younger wearers, lower rise.
• Midi: everyday coverage with a mid-rise fit.
• Full brief: heavy flow, overnight, maximum coverage.

Fit rules that stop leaks before they start

A period brief only works if the gusset sits flat against your body. If the leg openings gape, fluid will travel sideways instead of into the absorbent layers. If the brief is too tight, the fabric pulls and creates gaps at the crotch. The right fit feels snug but not compressive, with no wrinkles across the gusset when you stand and move.

Size for your current body, not the size you wore two years ago or the size you plan to be. Reusable period underwear does not stretch out like disposable pads, and a poor fit is the number one cause of leaks. If you are between sizes, size up for full briefs and stay true to size for bikini and midi styles, which have more give.

• Check the gusset in a mirror: it should sit flat with no gaping.
• Wash new briefs before first wear to check for shrinkage or fit changes.

How many pairs you actually need

A common mistake is buying seven identical pairs. Instead, build a small set by flow: two or three high-capacity briefs for your heavy days and overnight, and three or four lighter briefs for the rest of your period. That mix covers a full cycle with fewer pairs and less laundry pressure.

If you are new to reusables, start with one high-capacity pair and one light pair. Wear them on a day when you are at home so you can check the fit and absorbency without stress. Once you know what works, add more of the same style rather than experimenting with every option at once.

• Minimum starter set: 2 heavy, 3 light.
• Add one swim-specific pair if you swim during your period.

Decision rules for buying period underwear by flow

• If your heaviest day needs a super tampon plus a pad: Choose a brief rated up to 40ml with a full brief shape, such as the LBL Full Brief. The higher capacity and sealed seams reduce the risk of overflow on your heaviest days. Buy at least two of these so one can be washing while you wear the other.
• If your flow is light or you want backup: Choose a brief rated around 15–20ml, such as the Teens First Period Shortie for younger wearers or a bikini style for adults. These are thinner and more comfortable for light days. Light briefs are also useful as backup on heavy days if you prefer a pad-free option.
• If you are active or wear briefs all day: Prioritise stretch and a midi or full shape. The Superstretch Period Midi Brief is designed to move with your body, which keeps the gusset in place during sport and long days. Fit matters more than brand here: a gaping gusset will leak no matter how many layers it has.
• If you swim during your period: Do not use a standard period brief in water. Choose period swimwear with water-repellent fabric, like the Adult Period Swim Full Brief, which is built for in-water protection. One swim-specific pair covers most casual swimming needs.

Product facts that help you decide

• LBL Full Brief - Black: Absorbs up to 40ml (8 teaspoons) with 5 clever layers and patented sealed seams. This is the highest-capacity option in the supplied range, making it the practical choice for heavy flow days, overnight use, or anyone who wants extra reassurance.
• Teens First Period Shortie - Black: Made in junior sizes with 4 layers of absorbency and protection. The junior sizing and lighter layer count suit younger or smaller bodies and lighter flow, so it is a better starting point for tweens than an adult full brief.
• Superstretch Period Midi Brief - Black: Features SuperStretch technology with 4-layer period protection and a midi silhouette. The stretch fabric adapts to movement, which reduces bunching and makes this a strong everyday option for active days or medium flow.
• Adult Period Swim Full Brief - Dusk: Water-repellent fabric with 4 clever layers of protection, designed to be worn in the water. Standard period briefs are not made for swimming, so this is the correct choice if you want protection in the pool or sea.

Who this guide is for

Best for

• Anyone buying their first period underwear and unsure which absorbency to choose
• People with a mixed cycle who need both heavy and light options
• Parents buying for tweens or teens who need junior sizing

Not for

• Shoppers looking for disposable pads or tampons
• Anyone needing medical advice about heavy bleeding; see a doctor instead
• People who want a single pair to cover every day of their cycle without changing

Buy for your heaviest day first, then add lighter pairs for the rest of your cycle. Check the ml rating and layer count together, make sure the gusset sits flat, and start with a small mixed set before committing to a full drawer. That approach keeps leaks down and wasted spending to a minimum.