Comparison Table

Start with our own models, then see how active cooling compares with the other four ways of keeping medication cold away from home.

2–20 °C

Set any point from fridge-cold to room-cool. Everything else in the category is built for one fixed range.

No freezer

Cools from any power source in 15–20 minutes. Gel and biogel need 6–12 hours in a freezer first — every time.

You can read it

A real-time LCD. With a passive cooler you are trusting a gel pack that tells you nothing.

Our models

	EntryCB03	SmallestCB01	Best sellerCB02	LargestCB04
Best for	A short day out	The everyday carry	Most trips — size against capacity	Weeks away, or a protocol kept at home
Price	$89.99	$99.00	$139.99 ~~$169.99~~	$119.99 ~~$149.99~~
Capacity	250 ml · 3 pens or 8 vials	390 ml · 7 pens or 10 vials	600 ml · 12 pens or 20 vials	12 pens, or 7 biologic auto-injectors
Temperature range	0–18 °C (32–64.4 °F)	2–20 °C (36–68 °F)	2–20 °C (36–68 °F)	2–20 °C (36–68 °F)
Cooling system	5 V semiconductor	12 V semiconductor	12 V semiconductor	Semiconductor · 12/24 V adapter
Chamber volume	250 ml	390 ml	600 ml	793 ml — the largest
Internal dimensionslength × width × depth	175 × 58 × 25 mm	179 × 73 × 30 mm	180 × 74 × 46 mm	185 × 102 × 42 mm
Internal depthcan a small vial stand up?	25 mm — vials lie flat	30 mm — vials lie flat	46 mm — vials stand	42 mm — vials stand
Internal widthside-by-side room for bulky auto-injectors	58 mm	73 mm	74 mm	102 mm — 38% wider than CB02
Temperature display	Yes LCD	Yes LCD	Yes LCD	Yes LCD
Batteries	One, swappable · 10,600 mAh	One, swappable	One, swappable · spare sold separately	Two included · 13,600 mAh
Away from power	4–6 h	5–8 h per battery*	5–8 h per battery*	5–8 h × 2 batteries*
Power options	Wall · car USB	Wall · car	Wall · car	Wall · car · USB — runs from a power bank
Cools in	14 min	14 min	14 min	14 min
Warranty / returns	12-month / 30-day	12-month / 30-day	12-month / 30-day	12-month / 30-day

Same cooling system, different chambers. They differ in how much they carry and how long they last away from a socket — choose on what you pack, not on cooling performance.

On shape, not just size. CB02 and CB04 are both deep enough for a small vial to stand upright rather than roll; CB01 is not, so its contents lie flat. Where CB04 pulls ahead is width — at 102 mm it is 38 % wider than CB02, which is what lets bulky biologic auto-injectors sit side by side instead of making you choose between them.

How active cooling compares

	ActiveZKSCool	Powered + gel hybrid	Evaporative wallet	Gel-pack case	Bag + ice packs
Cooling method	12 V thermoelectric, cooling the whole time	Electric on power; frozen biogel once unplugged	Evaporation — cools relative to the air	Insulation only — slows warming	Insulation plus frozen packs
Set a temperature	Yes any point 2–20 °C	No cold only	No depends on the weather	No	No
Holds 2–8 °C	Yes indefinitely on power	While the pack stays frozen — 28–52 h at 86 °F	No holds roughly 25 °C	Warming from the moment it leaves the freezer	Uncontrolled
Holds 8–20 °Cfor anything labelled “do not refrigerate”	Yes on the dial	No	No	No	No
Needs a freezer first	Never	Yes, before every trip	No — but it needs water	Yes, before every trip	Yes, about 12 h ahead
Temperature display	Yes real-time LCD	Sometimes	None	None	None
Away from power	5–8 h per battery* — batteries swap in seconds	Longer on one frozen pack, then it needs a freezer	Two to four days per soak	Commonly claimed 4–12 h	Typically 4–12 h claimed
Freezing risk	None a thermostat holds the floor	Real, against a frozen pack	None	Real, against a frozen pack	Real — a pen touching a frozen pack can drop below 0 °C
Ready to go in	15–20 min from any socket	Freezer time plus a pre-cool	Soak and wait	Freezer time	Freezer time

The honest trade-off on biogel

A frozen biogel pack will outlast a single battery charge. The question is what happens next — biogel sends you looking for a freezer, which most hotels, offices and long-haul flights do not have. A battery swaps in seconds.

Evaporative wallets do a different job

Light, cheap and genuinely useful for a day out. They keep a pen below a hot ambient, but they do not reach the 2–8 °C a sealed insulin box is labelled for — and they never tell you what temperature they reached.

Too cold is the real danger

Unopened insulin tolerates room temperature for weeks. Freezing ruins it instantly, and you cannot see it happen. A bag of ice packs has no floor. A thermostat does.

“15 flights across Australia, Fiji and New Zealand over two months — humid tropics to southern-hemisphere winter, and not one out-of-range reading.”

Donna, ZKSCool customer. Her previous cool packs lasted about four hours.

*Battery runtime varies with ambient temperature, load, use and power source. Figures for other cooling types are typical ranges drawn from manufacturers’ published materials as of July 2026 and vary by product. Always follow your medication label and the advice of a healthcare professional — storage requirements differ by medication, and some products are labelled “do not refrigerate.”