The Science Behind Capsel™
Let’s dive into how Capsel works. At Marimo Labs, we’re always looking for innovative ways to improve product performance, and this starts with physics. Keeping your medications cool comes down to thermodynamics:
Keep the heat out with insulation
Absorb leaked heat with heat sponge phase-change materials
Keep the heat out: performance insulation
Using premium insulated tumblers like Stanley® and YETI®
Modern double-walled, vacuum-insulated stainless-steel tumblers already do a great job of reducing heat transfer. With Capsel, you have your choice of premium tumblers and bottles in dozens of colors, which you can use for beverages one day while protecting your medications the next.
Fixing the weak spot with a focus on safety
The lids of these tumblers are their weak spot. For life-saving medications like epinephrine, reliable access is critical, which means a large container opening. The last thing you want in an anaphylactic emergency is for an EpiPen® to be jammed in a narrow bottle neck.
Wide openings ensure immediate access to life-saving medications
Capsel insulates this wide opening with custom-fit caps that have internal insulating air cells. Capsel’s patent-pending cap is shaped to be easier to open than to tighten down. Standardized holders for location trackers like AirTag® and external badges for clear identification round out Capsel’s safety-driven design.
An in-progress picture shows how additive manufacturing builds insulating air cells right into each part
Absorb leaked heat: phase-change materials
Even the best insulated tumblers still leak heat. The second part of Capsel’s thermal protection is specially-formulated “heat sponges” made from phase-change materials, which absorb leaked heat so your medications don’t.
The science of phase-change materials
Phase-change materials, or PCMs, absorb and release heat through a process called a phase change—think of ice melting and refreezing. PCMs absorb thermal energy when they change from solid to liquid and release it when they return to a solid state, and they do this at a fixed temperature. In technical terms, we take advantage of large enthalpy of fusion to absorb heat.
Packets of PCM hug your medications. They start solid (white) and turn liquid (clear) as they protect your medications from heat.
Why we don’t just use ice to keep meds cool
With ice, the phase-change temperature is 32ºF (0ºC), which causes several problems.
Ice is so cold that condensation will form and medications can freeze.
Ice absorbs heat and loses its “charge” even when your medications don’t need it, so the timer is ticking right away.
You have to “recharge” it after every use
How Capsel uses phase-change technology
Capsel’s phase-change material (PCM) is designed to melt at 82ºF (28ºC)—just above room temperature. That means it starts absorbing heat as soon as things warm up, keeping the inside cool without needing batteries, ice packs, or electricity.
Why does that matter?
Many medications—like insulin, Ozempic, Wegovy, and epinephrine auto-injectors—should stay below 86ºF (30ºC). (See IAQ1, below). Capsel’s PCM melts a few degrees before that, pulling heat away and helping maintain a safe internal temperature even when it’s sweltering outside.
You can see in the data below that even though the environment is 44ºC (111ºF), the medications stay below 30ºC for over 360 minutes - that’s six hours. You can see the effect of the PCM kicking in around minute 60, where the rise in temperature just underneath the cap starts to flatten. That’s the PCM absorbing heat.
Thermal testing of Capsel with a 14oz Stanley® Tumbler
As long as the environment is cooler than 28ºC (82ºF), the PCM stays “charged.” Once it gets warmer, the PCM kicks in, absorbing heat and keeping your meds protected. When you’re back in a cooler space, it resets automatically. No freezing, no recharging—just ready when you are.
What’s it made of?
Capsel uses a paraffin wax blend made in the USA from American-sourced materials. It’s non-toxic, inert (like candle wax), TSA-friendly, and safe to be near sensitive meds.
Capsel’s PCM is encased in tough plastic packets and protected by a rigid frame. You can always see the charge state of your PCM and it can be easily inspected.
Designed with care
Capsel combines smart insulation, sustainable materials, and thoughtful design to make medication storage simple and reliable—no ice, no fuss. It's made in partnership with patients and families, using upcycled premium tumblers and responsibly sourced components.
This is the kind of practical innovation we strive for at Marimo Labs.
Our fair city
Infrequently Asked Questions (Because details matter)
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IAQ1: The USP Controlled Room Temperature (USP CRT) specification applies to many medications, for varying periods of time. Generally speaking, USP CRT specifies a storage temperature of 20-25ºC (68-77ºF) with excursions permitted between 15-30ºC (59-86ºC). Epinephrine auto-injectors like EpiPen® should always be stored at CRT. Other medications can be stored at CRT for a limited time. For example, Humalog insulin can be stored for up to 28 days at 30ºC, but Novolog 70/30 insulin should be used within 14 days. Ozempic should be used within 56 days of being removed from the refrigerator.
