The Everyday Thong

Core :

Limited Edition :

Size :

Size guide

XS S M L XL XXL

Product fit

-15%

-20%

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Our Everyday Thong in [Black/ Lilac/ Sand/ Butter/ Taupe], now with HeiQ Skin Care™ technology. A clinically tested synbiotic treatment infused in the fabric that helps restore your skin's natural balance, promote a healthier skin appearance, and strengthen your skin's protective barrier. No extra steps. Just wear it.

The Everyday Thong is a mid-rise thong designed for invisible, all-day comfort. The ultra-soft modal fabric and flat leg elastics mean zero visible panty lines under any outfit, including tight-fitting dresses, leggings, and light fabrics. The wider waistband sits securely without cutting in, and the longer gusset provides extra protection.

• Style: Mid-rise thong, minimal coverage

• UNDERskin™: 100% biobased synbiotic technology, supports your skin's natural microbiome, lasts up to 40 washes. Data provided by HeiQ based on testing conducted on other materials.

• Rise: Mid-rise but can be adjusted to your preference

• Coverage: Minimal back coverage

• VPL (Visible Panty Lines): None — this is Underdays’ best option for zero VPL

• Best For: Daily wear, under tight clothing, dresses, leggings, light fabrics

•Fabric: 92% TENCEL™ Micromodal, 8% Elastane

•UNDERskin™: Prebiotics + probiotics infused in the fabric transfer to your skin on contact, supporting a balanced, healthy-looking microbiome. 100% biobased. Powered by HeiQ Skin Care™.

•Sustainability: Our underwear is made from TENCEL™
Modal, sustainably derived from trees and twice as soft as cotton. Gentle on the skin and made to feel like nothing at all.

•OEKO-TEX certified: All of the fabrics we use are independently certified by OEKO-TEX (SH015 210990 Testex), meaning all our underwear is free from harmful substances.

•Waistband: Wide, soft self-fabric, no-dig, no-roll

•Gusset: Extra-long

•Leg Elastic: Flat comfortable elastic for no VPL

•Care: To preserve the HeiQ Skin Care™ treatment, wash at 30°C on a gentle cycle. The synbiotic technology is designed to last up to 40 home washes. Data provided by HeiQ based on testing conducted on other materials.

We also recommend to wash your Underdays in a mesh laundry bag. Air-dry flat in a shaded area. Do not bleach. Do not iron or tumble dry.

We offer both Next Day Delivery and Standard Delivery

Size down for a snugger fit, size up for a more relaxed fit.
Exchanges available if the size isn’t right.

View size guide

Select size

your underwear deserves better

You care about your skin, your wellness, your rituals. We’re pioneering care for your most intimate parts.

Powered by UNDERskin™

Prebiotics and probiotics, infused into the fabric, transferring to your skin all day. Supports your microbiome. Strengthens your skin barrier. Promotes a healthier appearance. 100% biobased. Developed in Switzerland.

Twice the softness of cotton

Our underwear is made from TENCEL™ Modal—sustainably derived from trees and twice as soft as cotton. Gentle on the skin and made to feel like nothing at all.

Let your ____ breathe freely

TENCEL™ fibers are unfavorable for bacteria growth. They wick away moisture and keep you fresh through the day. Designed to help reduce the risk of unwanted infections.

OEKO-TEX Certified

OEKO-TEX® certified —clean, non-toxic with no harmful substances

set apart by design

High Street Brand

TENCEL™ modal antimicrobial fabric derived from trees

Synthetics

Prebiotics + probiotics infused in the fabric for a healthier skin microbiome

Tested by real women, with over 1,000 five-star reviews

Engineered for optimal airflow and breathability

Traps moisture

A 2cm extra-long gusset for everyday protection

Soft leg elastics designed to eliminate digging in

Harsh seams

rebalance

Helps restore the natural balance of your skin microbiome.

radiance

Promotes a healthy skin appearance thanks to pre+probiotics.

protect

Strengthens your skin's natural protective barrier.

nourish

Feeds your own, native good microorganisms.

consistent

No change to handfeel, breathability, colour, or wicking.

100% biobased
Certified biodegradable
Clinically tested
Compliant with EC Cosmetic Regulation No 1223/2009

frequently asked questions

Our Everyday Collection is treated with HeiQ Skin Care™ — Swiss synbiotic technology that supports your skin's microbiome through fabric-to-skin contact. Underwear that works like skincare. It's a cosmetic treatment that promotes promotes healthy skin appearance, not a medical product, it doesn't diagnose, treat, or prevent disease. UNDERskin™ is embedded directly into the fabric during production, so it's working from the very first wear. No creams, sprays, or steps required.

No change to handfeel, breathability, colour, or fit, it feels exactly like the Everyday you already love. Non-irritant, human skin patch tested, and all ingredients INCI-listed.

Please check out our size guide above. We offer free exchanges on unworn items, so if the fit isn't right you can swap for a different size hassle-free. Not feeling it at all? We accept returns within 30 days of purchase.

Yes. The Everyday Thong is Underdays’ best option for minimal panty lines under any outfit, including white, thin, or body-hugging fabrics.

The Everyday Collection is ultra-soft modal — perfect for daily wear under work clothes, jeans, and dresses, and light activity like walking or gentle yoga. The Workout Collection uses moisture-wicking performance fabric designed to handle sweat and movement. Same flattering shape, but for anything higher intensity — running, HIIT, hot yoga — the Workout Thong will keep you drier and more comfortable.

Our core colours such as Black and Sand are always available and restocked regularly. Fashion colours and seasonal drops are limited edition — once they sell out, they won't be coming back. If you spot a colour you love, we'd recommend grabbing it before it's gone. Follow us on social or sign up to our mailing list to be the first to know when new colour drops land.