Frequently asked questions

Most containers are either toxic, ugly, or both. STAK uses borosilicate glass bodies and PFAS-free Tritan lids — materials that are genuinely clean, not just marketed that way. On top of that, the modular design actually stacks. No Tetris required.

PFAS (per- and polyfluoroalkyl substances) are synthetic chemicals used in thousands of products, including most food containers. They're called "forever chemicals" because they don't break down — in the environment or in your body. They've been linked to thyroid issues, certain cancers, and immune disruption. Most people have no idea they're storing their leftovers in them.

On August 12, 2026, the EU's updated food contact materials regulation comes into force, restricting PFAS use in containers, packaging, and cookware. STAK was designed around this standard from day one — not as a response to the ban, but as the thing the ban was pointing toward.

Container bodies: borosilicate glass (Grade 3.3) — the same glass used in lab equipment, chosen for its purity and thermal resistance. Lids: Tritan copolyester, a BPA-free, PFAS-free material that's shatter-resistant and dishwasher safe. Seals: food-grade silicone, PFAS-free.

Dishwasher safe: yes, both the glass body and the Tritan lid. Microwave safe: glass body yes, lid no — remove it before microwaving. Oven safe (glass body only): up to 300°C.

Yes. The silicone seal creates an airtight close. We tested it in every orientation — upside down, on its side, in a bag. If it leaks, that's on us.

Yes. Borosilicate glass handles thermal shock well — fridge to room temperature to oven isn't a problem. For the freezer, leave a little headspace if you're storing liquids (they expand).

We're launching EU-wide. Netherlands is our home market, with same-day delivery available in Amsterdam at launch. International shipping is on the roadmap — join the waitlist and we'll tell you when your region is live.

Netherlands: 1–2 business days. EU: 3–5 business days. All orders are processed within 1–2 business days of placement.

30 days from delivery, no questions asked. Unused and in original packaging. Email hello@stakcontainers.com with your order number and we'll sort it.

All major credit and debit cards, PayPal, Apple Pay, Google Pay, and iDEAL. More options coming.

If your order hasn't shipped yet, email hello@stakcontainers.com with your order number and we'll do our best. Once it's with the carrier, we can't intercept it — but our 30-day return policy has you covered.