Oct 23, 2025
Flex, the company that redefined menstrual products, didn't just appear. Before its massive success, it was a bold idea distilled into a compelling application for Y Combinator. That application, which secured Flex a spot in the prestigious accelerator, is a masterclass in clarity, persuasion, and understanding the problem you solve. This breakdown will show you how to apply those same principles to your own YC application.
The YC Application
Here is the exact application that got Flex into YC. Read it carefully. Notice how every word serves a purpose.
Company
Describe what your company does in 50 characters or less.
We make FLEX, a more comfortable alternative to tampons
What is your company going to make? Please describe your product and what it does or will do.
FLEX™ is a disposable feminine hygiene product. It’s shaped like a diaphragm, used for mess-free period sex, and can be worn in place of traditional menstrual products.
The menstrual products we use today were created in the 1930’s. They’re uncomfortable, disruptive, and inconvenient. 91% of women say they want alternatives, yet the $15B market for feminine hygiene continues to grow.
FLEX is worn internally, was designed for 12 hours of wear, and has the added benefit of mess-free period sex. It is disposable, is not linked to toxic shock syndrome, and is so comfortable, women tell us that they forget that they’re on their period when wearing it.
Founders
Please tell us about an interesting project, preferably outside of class or work, that two or more of you created together. Include urls if possible.
Our team is based in San Francisco but one member (Whitney) lives in L.A. We’re always looking for ways to save money on gas or flights. I came up with a concept for a DJ set and pitched a popular S.F. nightclub. I had never done anything like this but I managed to successfully broker a deal that paid for Whitney’s flight and her time. Plus, we had enough money remaining to purchase product samples and business cards! She played a sold-out show with another popular DJ and we took the opportunity to promote FLEX, gain trial sign-ups, and give away product samples.
How long have the founders known one another and how did you meet? Have any of the founders not met in person?
I’m a sole founder with a strong team of two full-timers, six freelancers, and four hard-working advisors.
AJ Forsythe of iCracked (YC W12) knew I was looking for someone with ecommerce acquisition experience and introduced me to his friend, Erika Jensen, who has 10 years of ecommerce business, most recently at JimmyJane leading marketing and acquisition efforts. She joined us in summer 2015 and has been building our ecommerce website and will be leading our online acquisition efforts.
Panpan Wang has a background in health as an entrepreneur and investor. He’s been working with me on FLEX since January 2015 in a working advisory role and has seen the company grow from pre-pitch deck to what it is today. Over the last two months, he’s taken a more active role. He’s also my life partner and quit his VC role in SF to move to LA and help me grow the business. We’ve been friends for over two years and have dated for one year.
Progress
How far along are you?
April marks our 1 year anniversary and we’ve raised $225k.
Key milestones:
We’ve run product trials with over 200 women
In the last 3 months, we’ve acquired 20,000 signups of customers who want to try FLEX
$0 spent on acquisition
We continue to grow with 1,000 trial signups each week
25% of our signups are men
How long have each of you been working on this? How much of that has been full-time? Please explain.
I’ve been working on FLEX for over 1 year. Our product is fully designed and ready for manufacturing. We have a supplier contract drafted and we’re currently working to close with a North American contract manufacturer.
In April, we launch preorders
In September, we ship to customers
In 2017, we expand to retail
If you are applying with the same idea as a previous batch, did anything change? If you applied with a different idea, why did you pivot and what did you learn from the last idea?
This is my second time applying to YC. (I was in the Fellowship W16 batch)
If you have already participated or committed to participate in an incubator, "accelerator" or "pre-accelerator" program, please tell us about it.
I received funding from Amplify.LA. They’re not a true incubator; they provide funding and free office space, but no programming or time limit.
Idea
Why did you pick this idea to work on? Do you have domain expertise in this area? How do you know people need what you're making?
I picked this idea for three reasons:
I hate tampons and like many women, I’ve spent a quarter of my life in discomfort caused by traditional menstrual products. In addition to physical discomfort, I’ve always been bothered by the social stigma that surrounds menstruation and period sex. Couples are missing out on 23% more opportunities for sex, and the great tragedy is that this is the time of month when women want it most. If women weren’t ashamed to talk about their periods, I’m certain we’d have better alternatives to the products that we use today.
NPR called 2015 the “Year of the Period.” We have reached the tipping point of a global menstruation movement. Women are trying “new” products like menstrual cups, period panties, and tampon subscriptions, but these solutions have come with a new set of challenges and frustrations. Women (particularly millennials) are demanding new product innovation and are open to trying brands that resonate with them more than ever before. 91% of women want a tampon alternative (Journal of Women’s Health).
In the product development process, we discovered an old patent for a product that’s been completely neglected by a small, private drug company (the company is focused on making a lubricant that’s more profitable for them). This product has 20 years of post-clinical research for us to draw from, and we’ve been able to use samples of this product for user research with over 200 women. We’re using this product for the basis of our product design, which allows us to move very quickly, streamline the FDA regulatory process, as well as expensive design iterations with manufacturers. We’re making a few improvements to differentiate the product (better fit/materials, more environmentally friendly, and made in the USA).
We have the perfect experience building brands and e-commerce platforms to bring this product to market in a completely new way that resonates with millennials.
We have 30 years’ experience using products we loathe.
I have ten years of experience launching consumer brands and communications strategies at companies like Coca-Cola, Autodesk and Upwork.
Erika has ten years of e-commerce experience. Most recently she grew e-commerce sales at JimmyJane from roughly $X to $Y in 1.5 years with a $0 budget.*
Our advisory team is hard-working and each member has 15–20 years of expertise in related fields: board certified OB/GYN, consumer e-commerce/subscription, healthcare manufacturing and supply chain, healthcare venture, and engineering.
What's new about what you're making? What substitutes do people resort to because it doesn't exist yet (or they don't know about it)?
What’s new about FLEX:
The distribution channel (e-commerce, direct to consumer, subscription)
Chic design, high-end packaging, differentiated branding and unique millennial voice
Product features (fit/materials)
It can be worn up to 12 hours and it is not linked to TSS
23% more sex; it allows a user and their partner to engage in mess-free intercourse (and if her partner is male, he won’t feel much, if anything)
Environmental impact (fewer changes, less packaging and waste)
This market is extremely underserved; women who don’t want to use tampons or pads have very few options other than menstrual cups.
There’s are a couple of important differences between FLEX and menstrual cups. Menstrual cups block the vaginal canal (don’t allow sex), they fill up and must be rinsed and reused. This makes for an awkward experience at work or in a public restroom. Menstrual cups are also difficult to insert (there are four different ways you can fold it before inserting) and remove (mine got stuck), which are huge barriers to adoption. Finally, menstrual cups are reused for 5–10 years, and this is a huge behavior change from disposing tampons. FLEX is disposable and addresses this important concern.
Who are your competitors, and who might become competitors? Who do you fear most?
Our competitors include large consumer goods companies and menstrual cup manufacturers.
We fear large consumer goods companies most: P&G (Tampax, Always), Kimberly-Clark (Kotex), Playtex Products, Energizer (o.b., Stayfree, Always). They have significant resources and channel relationships, but they also lack a standout brand; they don’t have a voice that resonates with millennials.
Softcup is another competitor* to watch because their product design is most similar to ours. Their awareness is very low, our brand is highly differentiated, and we’ve created an entirely different distribution strategy (direct to consumer, subscription-based with higher margins than traditional retailers).
Major menstrual cup manufacturers are competitors (DivaCup, Lunette) because they share many of the same benefits of our product and they have been in the market since the early 2000’s.
Finally, startups like white-labeled tampon subscription companies (LOLA, Cora) and absorbable period panties (THiNX, Dear Kate) are gaining momentum with millennials. The products aren’t new, but they have brands that engage millennials.
What do you understand about your business that other companies in it just don't get?
Women (and men) love our branding and positioning. 25% of our signups are from men. We’ve found a way to stand out amongst the cheap, pink-and-purple packaging of traditional feminine hygiene products, and our messaging (mess-free period sex) has been an effective hook to get women to try our product for the first time.
Once women try FLEX, they want to switch to FLEX permanently for a few reasons:
When women wear a pad or tampon, it’s a constant reminder that they’re undergoing this really uncomfortable experience
FLEX is so shockingly comfortable that women tell us that they forget that they’re on their period when wearing it
Instead of running to the bathroom 4–5 times per day to change a leaky tampon, FLEX requires changing only once every 12 hours
It’s very easy to use
In addition to a high-quality product, we’ve created a quality customer experience online. Most menstrual product purchases happen in drug stores, but drug stores don’t facilitate discovery of new feminine hygiene products. Millennials read and shop online, and we’ve created an e-commerce platform that educates them with peer-generated reviews and content.
Women learn about feminine hygiene products from their friends. The bulk of our early traction (20k organic signups) have come from word-of-mouth. On average, every person that signs up to try FLEX, recommends us to at least 1 additional person. Our campus ambassador program is one great example of our grassroots marketing efforts.
How do or will you make money? How much could you make?
We’ll sell monthly subscriptions of FLEX through our own e-commerce website; subscriptions will include free shipping for subscribers.
The global feminine hygiene market is over $15B and growing; the U.S. tampon market is $4B and growing. We aim to capture $3M in revenue during our first two years and see ourselves as a $100 million company in 5 years (similar to Dollar Shave Club).
How will you get users? If your idea is the type that faces a chicken-and-egg problem in the sense that it won't be attractive to users till it has a lot of users (e.g. a marketplace, a dating site, an ad network), how will you overcome that?
Distribution: starting online/direct to consumer; we’ll also leverage existing relationships with online retail partners.
Awareness:
Earned: media & influencers - we’ve given samples to well-known women (media, bloggers, Instagram, founders) and we will run a hero campaign featuring them, and seek a celebrity endorsement; we’ll run an aggressive PR campaign for earned media
Paid: traditional online advertising (social media, Google Adwords); content networks
Owned: content & social - we’ll continue to write original content and contributed articles and share on social media
Grassroots efforts are the most important part of customer adoption; 79% of women say they’ve made purchases based on the recommendation of a peer, and 82% of women say they share brands and products with friends (Ladies’ Home Journal). This includes campus ambassador programs (sororities, sports teams, clubs), and direct selling
Samples and referrals: every new subscriber gets a free sample to give to a friend with discount code; we run frequent contests for online friend referrals
Equity
What kind of entity and in what state or country was the entity formed?
We are incorporated in Delaware as a C-Corp.
Legal
Are any of the founders covered by noncompetes or intellectual property agreements that overlap with your project? If so, please explain.
None of the team is under an overlapping non-compete.
Who writes code, or does other technical work on your product? Was any of it done by a non-founder? Please explain.
All code and intellectual property has originated from The Flex Company team members.
Is there anything else we should know about your company?
When making a purchasing decision, 73% of consumers care about the company, not just the product. Once we are profitable, we will donate a percentage of our profits toward a non-profit partner that furthers our social mission.
We’ll undergo B Corp Certification to hold ourselves to higher standards of transparency, accountability and performance. This designation is much like a Fair Trade or LEED certification and signals that we’re committed to making a profound social difference and safeguarding people and the planet, while remaining profitable.
While this will not change our legal standing as as a Delaware C Corp, B Corp Certifications are often confused with legally recognized Benefit Corporations. Other examples of certified B Corps include Patagonia, The Honest Company and Plum Organics (now owned by Campbell’s).
Others
Please tell us something surprising or amusing that one of you has discovered.
I’ve always gotten yeast infections for a full week after my period when using tampons, and I learned through speaking with hundreds of women that many have the same issue; a dirty secret tampon companies and women themselves don’t talk about.
After using FLEX many women - including Erika and I - no longer get post-period yeast infections.
This isn’t so much amusing as it is amazing.
Many of the women I speak with about their periods tell me that their mom started them on pads… because if they used a tampon, they “wouldn’t be a virgin anymore.” Women are always surprised at themselves for saying that. I think we don’t realize that period stigma is so deeply ingrained in us.
Curious
What convinced you to apply to Y Combinator? Did someone encourage you to apply?
Several of our friends have founded YC companies (e.g., StyleLend, iCracked, Airhelp, Her). We’ve seen the positive impact that their experience has had on their businesses. Our desire to accelerate growth of the business and the strong recommendation of these founders motivated us to apply.
General advice
Be as concise as possible. 1–2 sentences is best.
For any answers that require more than a couple sentences, the first sentence should act as a TL;DR.
Heavily optimize for clarity. Reviewers shouldn’t need to read a sentence twice, or look anything up to understand your answers.
Avoid marketing-speak and jargon.
Assume the reviewers have little-to-no domain knowledge.
Each answer should make sense on its own. Reviewers may not read every answer, and they may not read them in order.
Be honest. No need to exaggerate you answers, YC accepts companies of all stages and backgrounds.
Improving your company is a better use of your time than improving your YC application. Write your application, then get back to work.
Quick Takeaways
Lead with the Problem: Flex immediately highlights the shortcomings of existing products.
Show, Don't Just Tell: Instead of simply claiming traction, they provide concrete numbers (20,000 signups with $0 ad spend).
Know Your Market: Flex demonstrates a deep understanding of their target audience, their pain points, and the competitive landscape.
Have a Clear "Why": The founder's personal connection to the problem makes the mission authentic and compelling.
A Great Team is More Than Just Founders: Flex effectively showcases the expertise of their core team, freelancers, and advisors.
Conclusion
Your YC application is more than just a form. It's your first real test as a founder. Can you communicate your vision with clarity and conviction? Flex's application is a powerful reminder that the best way to do this is to focus on the fundamentals: a real problem, a smart solution, and a team that can execute.
So, what's next? Don't just copy and paste Flex's answers. Instead, use their application as a framework to tell your own story. What is the problem that you are uniquely positioned to solve? Who is the team that you have assembled to solve it? And what have you already done to prove that you're on the right track? Answer these questions with the same honesty and clarity as Flex, and you'll be well on your way.
FAQs
1. How important is it to have traction before applying to YC?
Traction is always helpful, but it's not a deal-breaker. As Flex's application shows, early traction (like their 20,000 signups) can be a powerful signal. If you don't have revenue yet, focus on other metrics that show progress, like user growth, engagement, or letters of intent.
2. What if I'm a solo founder?
While YC has a reputation for preferring teams, solo founders are accepted. Flex's application is a great example of how to address this. The founder, Lauren Schulte Wang, immediately follows up her statement about being a sole founder by highlighting the strength of her extended team.
3. How much detail should I go into about my competitors?
Be honest and direct. Acknowledge your competitors, but don't obsess over them. Flex's application does a great job of this by identifying their main competitors and then quickly pivoting to explain how they are different.
4. Should I mention that I've applied to YC before?
Yes. Being transparent about a previous application is a good thing. It shows persistence and a long-term commitment to your idea.
5. How much does the "voice" of the application matter?
It matters a lot. Your application should sound like it was written by a human, not a committee. Flex's application is a great example of this. It's professional yet personal, confident yet humble. It's the voice of a founder who knows their business inside and out.
