Insulin and medicine cool bags compared: what keeps them cool in a power cut or heatwave

FRIO's Duo is an evaporative wallet: soak the inner pouch in water and the crystals in it swell into a gel that cools as the water evaporates, with no power or ice involved. Frio says it holds 18-26°C for at least 45 hours in constant 37.8°C air, then needs a re-soak, and that in-use insulin is fine in it for up to 28 days; your own leaflet's time and ceiling still come first. Frio says it takes two standard pens, one EpiPen, or a mix of vials and cartridges. It keeps a room-temperature band, not fridge cold.

Worth knowing: A room-temperature band, not fridge cold, so unopened spare stock that belongs at 2-8°C needs a different answer

Who shouldn't buy it: Your spare stock needs fridge-cold storage for days, or it is for EpiPens: the leaflet says not above 25°C and to carry two at all times, and Frio says the Duo holds only one. Ask your pharmacist first.

The Large is the same evaporative design as the Duo in a bigger pouch (about 20 x 13 cm inside, per Frio's size guide). Frio says it takes up to 5 standard pens, 5 vials or 10 cartridges, or up to 3 EpiPens, and quotes the same figures for every size: 18-26°C for at least 45 hours in constant 37.8°C air, re-soaked to restart. The leaflet gives it a longer soak of 14-18 minutes plus draining, so allow time to prepare it.

Worth knowing: Longer preparation: 14-18 minutes in water plus 15-30 minutes draining, per Frio's leaflet

Who shouldn't buy it: You carry one or two pens, because the Duo does the same job in a smaller pouch, or your spare stock must stay at 2-8°C.

The Extra Large is the biggest of the three Frio sizes here (about 20 x 16.5 cm inside, per Frio's size guide), taking up to 8 standard pens, 8 vials or 16 cartridges, or up to 5 EpiPens, per Frio. It has the same evaporative design and the same maker figures: 18-26°C for at least 45 hours in constant 37.8°C air, then a re-soak. Its soak is the longest, 15-19 minutes plus draining. Worth it only if the smaller pouches would not take what you carry.

Worth knowing: The longest preparation of the three: 15-19 minutes soaking plus draining, per Frio's leaflet

Who shouldn't buy it: The Duo or Large would take what you carry, since this is the most to soak and carry, or your spare stock must stay at 2-8°C.

4ALLFAMILY's Big Nomad is an insulated steel tube with a reusable Biogel pack that you freeze for 6 to 8 hours first. For the Large size the maker publishes a table: in 30°C air it says 2-8°C for 33 hours and below 26°C for 52 hours, easing to 28 and 46 hours at 40°C. These are the maker's own numbers with no named test, but it is the clearest published set among the ice-pack cases, and it aims at the 2-8°C range for unopened stock.

Worth knowing: 4ALLFAMILY says the Nomad is for refrigerated medicine only, not opened medicine kept at room temperature, and the Lantus SoloStar and Apidra SoloStar leaflets say a pen in use must not be refrigerated

Who shouldn't buy it: You want a wallet that needs only water, you are protecting a pen in use whose leaflet says no fridge, or you carry one or two pens and want something lighter.

BreezyPacks' Basic has a lining of phase-change material that, the maker says, sets at 27°C: below 24°C it stays charged, above 27°C it works to keep the inside between 25 and 27°C, and it recharges itself overnight in a cool room. BreezyPacks says it is for medicine in use only, does not get fridge-cold and gives no extra protection from cold. The maker's pages give no hours for the Basic; the Amazon listing says at least 6 hours at 38°C. The 25-27°C inside sits above the 25°C ceiling printed in some leaflets.

Worth knowing: The only hold time is a listing figure of 6 hours at 38°C; the maker's pages give no hours for the Basic

Who shouldn't buy it: You need fridge-cold storage, a long hold in extreme heat, or your leaflet's ceiling is 25°C; BreezyPacks also says it is for medicine in use only.

The Voyager Mini pairs a USB-powered cooling lid, which the maker says holds 2-8°C while it has power in air up to 35°C (8-26°C at 40°C), with a Biogel pack for no-power use, quoted at up to 30 hours of 2-8°C in 30°C air. It is the only case here that can hold fridge temperature for longer than a frozen pack lasts, but in a power cut only while a power bank or car socket lasts. 4ALLFAMILY says it is for unopened, refrigerated medicine, not opened pens kept at room temperature. Amazon's bullets say 7 pens; the maker's Mini page says 2 or 3.

Worth knowing: The powered mode needs USB in a power cut, and the maker quotes only 8-12 hours from its own 20,000 mAh bank

Who shouldn't buy it: It is for a pen in use (the maker says it is not meant for medicine kept at room temperature once opened), you want something that works with nothing charged, or you are not ready to keep a power bank topped up.

Medicool's Dia-Pak Deluxe is a padded nylon supply organiser with a refreezable gel pack, and cooling is secondary to carrying. Medicool says the pack keeps insulin and other medicines cool for up to 12 hours, but gives no air temperature for that figure and says the time varies with conditions. Nothing in it needs power or water, and it suits an afternoon out more than a long power cut.

Worth knowing: A single 12-hour figure with no temperature behind it, so the hold time in a hot room or a long cut is unknown

Who shouldn't buy it: You need a stated hold time at a stated temperature, or cooling beyond a long afternoon: Frio and the 4ALLFAMILY Nomad publish both.