Food ยท Gear Review
Insulated cooking bags. One real choice, and what to use instead.
A cooking bag wraps a pot you already own, so the heavy Dutch oven on your stove becomes a no-fuel slow cooker. In November 2026, the Wonderbag was the only purpose-built cooking bag we could find for sale to U.S. households, so this page compares its three sizes, then the homemade and rigid options that do the same job. For most families, the Wonderbag Medium is the one to get.
Top pick
Wonderbag Medium
Takes
Pans of 2 to 6 liters
Price
From about $135, delivered
At a glance: Wonderbag Medium
Strengths
- It wraps a pot you already own, so there is no new pot to fit your stove.
- Practical Sailor named it the best fabric bag it tested, especially for small pots.
- The medium size takes pans of 2 to 6 liters, the range most family pots fall in.
- Wonderbag says it can be spot washed or machine washed on a gentle cold cycle.
Limitations
- It ships to the U.S. from the U.K., one bag per customer, from about $135.
- It is bulky to store, and a new bag needs fluffing before first use.
- In one lab test, a chicken curry came out after four hours just one degree above 140 degrees F.
By Dan Whelan, founder of New World Survival
Researched from USDA, FDA, and CPSC guidance, maker documentation, published testing, and owner reports. See our sources
The one thing to know
The margin is thinner than the hours suggest.
Wonderbag says food keeps cooking in its bag for up to eight hours and stays warm for several hours after. (Wonderbag) Warm is not a food safety standard. USDA says bacteria grow fastest between 40 and 140°F, the danger zone, that hot food should stay at 140°F or above, and that food should not sit in that range for more than 2 hours, or 1 hour above 90°F. (USDA FSIS) In a 2014 test funded by the German development agency GIZ and run by a university in Bangladesh, a 1.1-kilogram chicken curry left four hours in a Wonderbag, in a room near 90°F, came out at 60.5°C, about 141°F. (GIZ) That is one degree of room.
So the rules that keep it safe are the rules for every retained-heat cooker. The pot goes in at a full boil all the way through, and an EPA design guide adds 10 to 15 more minutes of boiling for food in large pieces. (EPA) The FDA advises soaking raw red kidney beans at least five hours and boiling them in fresh water at least 30 minutes, and we give every dried bean that boil on the stove before it goes in. (FDA) Before serving, a food thermometer in the middle of the pot should read 140°F or above. Below that, if you cannot be sure it has been there less than two hours, throw it out.
Fill the pot. A nearly full pot holds heat longest, and Practical Sailor found a 1-quart pot cooled about twice as fast as a 4-quart one. (Practical Sailor) Our thermal cooker handbook covers the full food safety section and the temperatures to check.
The field
One bag, sized by the pot you own.
We looked for purpose-built cooking bags sold to U.S. households on November 8, 2026. The Wonderbag was the only one we found. Practical Sailor also tested a Heylo bag, which we could not find for sale in the U.S., and searches for cooking bags on Amazon returned casserole carriers and slow-cooker travel totes instead. Sizes come from Wonderbag, and the price from its store, which showed one starting price for every bag it listed.
Wonderbag Small
- Takes: pans up to 2 liters
- Feeds: one or two people
- Best for: a small saucepan of oats or rice
Wonderbag Medium
- Takes: pans of 2 to 6 liters
- Feeds: up to six portions
- Best for: the family Dutch oven or soup pot
Wonderbag Large
- Takes: pans of 6 to 10 liters
- Feeds: large families, batch cooking
- Best for: a big stockpot of stew or beans
Sources: sizes and servings from the Wonderbag FAQ; price from the Wonderbag store, from $135.45 including shipping and U.S. customs, read November 8, 2026. Larger sizes may cost more at checkout.
Our picks
Measure your pot, then choose once.
Wonderbag says it can send only one bag per U.S. customer for now, (Wonderbag) so the size decision matters more than usual. Measure the pot you cook in most, filled the way you usually fill it, and buy for that.
Top pick
Wonderbag Medium
A thick bag of re-purposed foam insulation in a polyester cover, (Wonderbag) with a padded top that goes over the lid and a drawstring that cinches it closed around the pot. (The Family Freezer) The medium takes pans of 2 to 6 liters, which covers most family Dutch ovens and soup pots. When Practical Sailor tested fabric bags, vacuum cookers, and homemade setups, it called the Wonderbag the best fabric bag choice for its versatility and efficiency, especially with small pots. (Practical Sailor) Wonderbag recommends pans of copper, steel, aluminum, cast iron, enameled cast iron, or glass. A heavy pot with short handles and a tight lid suits it best.
WonderbagFor big batches
Wonderbag Large
Pans of 6 to 10 liters, for a large family or a stockpot of beans or stew. Sous Chef, a U.K. cookware retailer, measured the large at about 47 by 47 by 22 centimeters when fully expanded, roughly 18 by 18 by 9 inches. (Sous Chef) Choose it only if you fill a big pot most weeks. The EPA guide says the pot should fill the insulated space with little air around it, (EPA) so a bag much bigger than your pot works against you.
WonderbagThe pot that goes in it
A heavy lidded pot
The bag is only half the cooker. A heavy pot holds more heat, and short side handles let the drawstring close tight; an owner on Wonderbag's own review page notes that long handles do not fit. (Wonderbag reviews) An enameled cast iron Dutch oven is the classic match. Our Dutch oven comparison covers the pots.
How we link here
No commission on this page
Wonderbag was not available on Amazon in the U.S. when we checked, so the links go to its own store and New World Survival earns nothing from them. Commission never decides a recommendation. One note on giving: older articles describe Wonderbag as buy one, give one. Wonderbag says it has moved away from that model and now uses part of its profits to subsidize bags for lower-income families. (Wonderbag)
What owners actually say
It works. It is also big.
These patterns come from sailing and cooking publications whose writers used one, retailer reviews, and Wonderbag's own review page, read November 8, 2026. Much of the U.S. owner discussion dates from years ago, when the bag was sold on Amazon here, so we weigh it with that in mind.
The results
The steady praise is tender stews, braises, and chicken without a stove left on. Good Old Boat's reviewer called it a capable replacement for a slow cooker aboard a boat. (Good Old Boat)
The trouble spots
Size is a common complaint. The author of The Boat Galley found it too big to keep aboard even squashed down, though Good Old Boat's reviewer stored it as a spare cushion. (The Boat Galley) Practical Sailor noted that a bag with a full pot inside is bulky to stow, and needs a secure spot to avoid hot spills. (Practical Sailor)
The surprises
A new bag arrives packed flat; Practical Sailor needed about 15 minutes of kneading to fluff one back up, and Wonderbag tells owners to work air into the foam on first use. (Wonderbag) U.S. owners who bought years ago got theirs on Amazon here; today it ships from the U.K.
How it fails, and what it costs over time
Scorches, spills, and soiled foam. Nothing to refill.
Scorching
A pot straight off the burner is hot enough to mark the lining. Wonderbag tells owners to lay a tea towel or wooden chopping board under the pot to keep the inside fabric from burning. (Wonderbag)
Spills and dirty foam
The EPA guide warns that soiled insulation becomes a health hazard, and that insulation must stay dry to work. (EPA) Keep the lid tight, add a towel around the pot, and wash the bag when it needs it.
Washing
Wonderbag says the bag can be spot washed and hung to dry, or washed in a front-loading machine on a gentle cold cycle with minimal detergent, then hung or tumble dried on low. (Wonderbag) Dry it fully before you close it up for storage.
The warranty
Wonderbag's FAQ lists no warranty terms. It says bags are checked before shipping, and that a faulty one can be reported through its contact form. (Wonderbag) With an overseas seller, keep your order details.
The running costs
None to speak of. There is no cord, no battery, and nothing to refill, and the pot is one you already own. The savings come from the fuel you do not burn: Aprovecho Research Center, a nonprofit that tests cookstoves, says a retained-heat cooker saves about half the fuel and time spent cooking. (Aprovecho) Our retained-heat cooking guide charts it food by food. The one purchase that comes with any cooking bag is a food thermometer.
What to use instead, and who should skip
The same idea, for less or for the road.
A homemade box or basket
In tests reported in the EPA guide, a wood basket lined with a wool blanket and a cardboard box lined with foam board both held 5-liter pots of boiling water between 80 and 85°C (176 to 185°F) after three hours, not far behind a purpose-built cooker, though the guide notes neither design holds up long in regular use. (EPA) It costs nothing, and it is the best way to learn whether the method suits you.
A picnic cooler and towels
The one household item big enough for a stockpot. Cooler liners are plastic and were not made as cookware, so we set the pot on a towel or wooden trivet, not straight on the plastic, and pack towels all around it. Our retained-heat cooking guide walks through it.
A rigid thermal cooker
A steel case with its own pot is easier to secure in a moving car, camper, or boat, and a vacuum-insulated one holds heat longer than foam. Our thermal cooker comparison covers them.
Casserole carriers and slow-cooker totes
Amazon sells many of these for about $15 to $27. They are made to carry a dish to a potluck. The listings we checked describe carrying and cleaning, not cooking, and none gave any heat-holding figure. Fine for the drive; not a cooker.
Skip it if your pots have long handles
A long-handled saucepan will not close inside the bag. If that is all you own, a homemade box sized around it, or a thermal cooker with its own pot, is the better start.
Skip it if you cook for one
Small portions cool fastest. For a single bowl of oats or soup, a wide-mouth vacuum jar holds heat better than a bag around a tiny pot. Our food jar comparison covers them, and what is safe to cook in one.
Where it fits in your readiness
Your own pot, turned into a fuel saver.
A cooking bag belongs to the Sustain tier: gear that keeps a household eating normally through a long disruption. It earns its place in a long power outage, a winter storm or ice storm, and the weeks after a hurricane, when every can of fuel has to stretch. If the boil happens on a camp stove or grill, that part stays outdoors: the CDC warns never to use gasoline, propane, or charcoal-burning devices inside a home, garage, or carport, or near doors, windows, or vents. (CDC) Once the pot is off the flame, the bag can come inside.
Power outage checklist
Cooking, food, and fuel when the lights go out.
Food preparedness checklist
The pantry and cooking basics that come first.
Retained-heat cooking
Five steps, the fuel-savings chart, and first-try mistakes.
Dutch oven cooking
Heavy, lidded one-pot cooking, and the pot a bag suits best.
Questions people ask
About cooking bags.
Can you buy a Wonderbag in the U.S.?
Yes, from Wonderbag's own store, which ships from the U.K. When we checked in November 2026, U.S. prices started at $135.45 including shipping and customs, and Wonderbag said it could send only one bag per U.S. customer. Its old Amazon listing read currently unavailable.
What size Wonderbag should I get?
Match it to the pot you cook in most. Wonderbag's small takes pans up to 2 liters, its medium takes 2 to 6 liters, and its large takes 6 to 10 liters. Most family Dutch ovens and soup pots fall in the medium range. Because U.S. buyers can order only one, measure your pot before you choose.
Is it safe to cook in a Wonderbag?
It can be, if the food goes in at a full boil and comes out at 140°F or above on a food thermometer. The bag adds no heat. In one lab test, a chicken curry left four hours in a Wonderbag came out about one degree above 140°F, so check every time. Dried beans, especially red kidney beans, still need a 30-minute boil on the stove first.
Can you wash a Wonderbag?
Wonderbag says it can be spot washed and hung to dry, or washed in a front-loading machine on a gentle cycle with cold water and minimal detergent, then hung or tumble dried on low. A towel under and around the pot keeps it cleaner and protects the fabric.
Is a casserole carrier the same as a cooking bag?
No. Casserole carriers and slow-cooker travel bags are made to carry a dish to a potluck. The ones we looked at describe carrying and cleaning, not cooking, and none gave any heat-holding figure. A cooking bag is much thicker, and wraps the pot on every side, including the top.