Every now and then I randomly hop on the internet or some online marketplace and I search “math” or “maths” followed by e.g. “clothing” and see what pops up, and over the years I’ve undoubtedly accumulated a bunch of maths-themed clothing that I’m now aware that other people are interested in acquiring.
One thing I will point out: I’m fundamentally against print-on-front-of-t-shirt designs because they’re too easily done-up and make up a lot of “fast fashion”. Arguably there’s the possibility that some stuff I’ve bought below are also from environmentally-unfriendly stores (e.g. AliExpress), so as always, please be cognizant of your own personal values.
So here’s a (definitely not going to be updated regularly) list of online stores of which I’ve bought from, click on the title or image for a direct link to their site and specifically to their maths collections:
AliExpress – Champagne Store
Some poking around on other entries might be needed to find all of those in the image below, but I own all the beanies below.

Geek Tropical
This one popped up on my Instagram ads and I took advantage of a special-day deal to grab both the left-most and right-most shirt from this collection. There’s also bucket hats!

Kudry Science Gift Lab
Looks like 1-2 maths-specific designs applied to a bunch of various merch: shirts, shoes, beanies, etc. I own the two beanies in the top left (and the white one allows you to insert a custom quote/message!)

FreshHoods
Select designs applied to shirts, hoodies and bomber jackets. They use dye-sublimination printing which is undoubtedly better than ‘pressing an image onto a shirt’-esque designs. I own the polo shirt on the left.

Other generic online marketplaces
Searching ‘math(s) clothing’ on e.g. Amazon, Temu, AliExpress, Shein, RedBubble and pretty much any other generic online marketplace will bring up plenty and it’s very easy to be spoilt for choice or buy too many, hence my preference for something more tightly curated and paying a bit more for ideally indie and local storefronts.
Wait I’ve seen you wear certain clothing that I can’t find anywhere?!
The clothing in the below picture, for example, was bought so long ago that upon digging through my emails, the storefronts they were brought from no longer exist 😟.
