Hair Theory Lab
Hair Theory Lab Serum-in Mask, 120g
Hair Theory Lab Serum-in Mask, 120g
Put an end to the memory of frizz. Environmental frizz and straightening mask.
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• Authenticity guaranteed.
• Ships direct from Japan in 3-5 days
• Custom duties & tariffs fully handled by us for US customers.
• Track your order via USPS, Royal Mail, Canada Post, Australia Post.
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What it is
Stubborn frizz and twists caused by damage from high temperatures, humidity, and UV rays. In fact, this "environmental frizz" takes three days to set in. So, before it sets in, use a serum-in mask every three days to intensively reset accumulated damage*. Formulated with a high concentration of "Tostea(R)" to strengthen hair density and care for frizz. It reinforces the bonds between amino acids that have been broken by damage, and approximately 90% of the beauty serum ingredients thoroughly repair the inside of the hair. It becomes smooth and manageable the moment you dry it. It feels supple and smooth every time you touch it. For beautiful hair that is not at the mercy of the environment. *Providing moisture and preparing the hair to be easy to manage.
Ingredients
How to use
After shampooing, lightly squeeze out excess water, apply the product to your entire hair, leave it on for 2-3 minutes, then rinse thoroughly. Use the appropriate amount according to your hair length: Short hair: about the size of a 100-yen coin Medium hair: about the size of two 100-yen coins Long hair: about the size of three 100-yen coins
We ship internationally from Japan!
Frequently Asked Questions
Are the products you sell authentic?
Authenticity is 100% guaranteed. We source directly from the brand, or from official stores within Japan.
All products are fresh off the shelves and never outdated.
What are your shipping rates?
On orders under US$75, shipping is a flat US$20 to the United States and US$10 to all other countries.
Orders of US$75 or more ship free, applied automatically at checkout. Your exact shipping cost is shown before you pay.
How long does delivery take?
These estimates are for International Airmail (Tracked) and include 3 to 5 business days of processing in Japan.
- United States: 12 to 15 business days
- Canada, United Kingdom, France, Germany: 9 to 12 business days
- Australia, New Zealand, Denmark, Finland, India, Indonesia, Italy, Netherlands, Spain, Sweden, Switzerland: 10 to 13 business days
- China, Hong Kong, Malaysia, Singapore, South Korea, Taiwan, Thailand, Vietnam: 8 to 10 business days
- Rest of the world: 11 to 18 business days
Actual delivery can be affected by customs clearance, seasonal congestion, or carrier delays in the destination country, all of which are outside our control.
Do you offer express shipping?
Yes. As of 22 July 2026, we offer International Express Mail through Japan Post. The cost is based on order weight and is calculated automatically at checkout.
Will I pay customs or import fees?
US orders: No. As of July 1, 2026, all US orders ship DDP (duties delivered prepaid), meaning we prepay all import duties on our end. Nothing is due at your door.
Orders outside the US: Possibly. Duties and import taxes are set by your local customs authority and are not collected at checkout, so any charges on delivery are your responsibility.
We're working on rolling out prepaid duties for more countries soon.