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Slow Cooking with the Amazing Wonder Oven

Avatar for Gaye Levy Gaye Levy  |  Updated: November 24, 2020
Slow Cooking with the Amazing Wonder Oven

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In the pursuit of self-sufficiency, Prepper’s are always looking for innovative ways to cook food.  Part of that comes from our desire to eliminate our dependency on fossil fuels and part, to be quite honest, has to do with the process of cooking itself.

Does it come as any surprise that some of the most popular preparedness and homesteading websites feature cooking and recipes?  We all love to eat and eating, for the most part, requires cooking.  In my own household, in addition to a gas stove-top, I use charcoal and wood-burning Volcano stove, an EcoZoom rocket stove that burns biomass, and two Solo Stoves.  I will surely run out of food before I run out of cooking facilities!

Wonder Ovens BDS

This brings me to the topic of today’s article which is slow cooking with the amazing Wonder Oven. Also known as a “hay box”, here is what Wikipedia has to say about the Wonder Oven:

“A hay box, straw box, fireless cooker, insulation cooker, wonder oven or retained-heat cooker is a cooker that utilizes the heat of the food being cooked to complete the cooking process. Food items to be cooked are heated to boiling point, and then insulated. Over a period of time, the food items cook by the heat captured in the insulated container. Generally, it takes three times the normal cooking time to cook food in a hay box.”

When I first heard the term “Wonder Oven”, I was curious and if I was curious, I knew you would be too.  Lucky for us, one of my blogging friends, Megan Smith at My Food Storage Cookbook, is an expert on wonder ovens and uses them daily while cooking meals in her own household.  She has generously offered not only to explain the Wonder Oven to us, but also to share how you can make or purchase one yourself.

With the assistance with Megan, let us begin at the beginning.

Wonder Ovens – What Are They?

Have you heard about Wonder Ovens and their capacity to conserve fuel in a survival situation?

A Wonder Oven (also called a Wonder Box, Hot Box or back in pioneer times a “Hay Box”) is a set of pillows, a larger pillow for the bottom and a smaller pillow to fit on top, which are filled with Styrofoam beads. These pillows are used to retain temperature for a long period of time.

While a Wonder Oven doesn’t actively heat the food to temperature, after it’s heated, it’s able to hold that temperature for many hours. Slow-cooking in style, it’s comparable to a “crock pot” but requires no power.

Wonder Oven pillows1

What’s the Secret?

It’s “Samson-like” strength — from a heat retention point of view– comes from what’s inside it: tiny (3mm) Styrofoam beads, which when pressed against themselves, work to create a Styrofoam wall where temperatures cannot escape.

While some Wonder Ovens are made with larger 5 mm beads, smaller sized beads have been shown to retain heat the longest.

Wonder Oven Styrene Pellets1

By understanding it’s mechanism for heat retention – creating a barrier with Styrofoam which traps heat – it’s easy to see how it works similar to a cooler. However, in this case, because the beads in the pillows fit directly around the source (creating a barrier right next to it) air gaps are eliminated.

All of this is available for very little cost.

The Power of a Wonder Oven for Emergencies

I’d like to begin by giving you an idea of what a Wonder Oven can do and a basic overview of how it’s used.

Let’s say a food item (a hot pot full of food, or something already cold or frozen) is nested within the pillows and very simply left alone. So long as the basic cooking rules are kept (details to follow) and it’s left undisturbed, it’s temperature is retained generally between 12-18 hours.

It’s effective, whether the temperature is boiling hot, cold or frozen.

Near Boiling Temperatures Are Retained for 12-18 hours

If you were to boil a pot of water following the basic usage rule I’ll share in a moment, and nest the pot so it’s surrounded by Wonder Oven pillows, the temperature of the water would be kept near boiling temps for longer than 12 hours. Because the boiling point is well above the “danger zone” food safety mark of 160 F, it’s a “food safe” option for cooking even though it’s without a fuel source for the many hours it cooks.

With this, you’re able to “fuel- afford” to cook in ways you never could have before. Beyond being able to fix amazing normal-tasting recipes thanks to a Wonder Oven, you will, in reality, most assuredly run out of stored fuel before running out of food in an emergency or survival situation.

Frozen Foods Are Kept Frozen for 12-18 hours

In traveling, I once placed frozen hamburger patties in the Wonder Oven to keep them frozen during a 12 hour road trip. Once we arrived I pulled them out and they were still frozen completely, just as if I’d pulled them straight from the freezer.

It was a pretty cool demonstration to show skeptical family members, but the reality is, it works!  I keep a set of Wonder Oven pillows in the back of my vehicle just for this reason. On a day to day basis, they’re fantastic for keeping frozen items from the grocery store frozen until I get home.

In the case of a power outage, having a few sets of Wonder Oven pillows available could keep the frozen items you have in the freezer from going to waste.

Cold Foods are Kept Cold for 12-18 hours

Having a Wonder Oven available to “keep cold foods cold” is better than any cooler because it doesn’t require any ice! As a busy mom I’ve appreciated using ours in this way especially on days where we’re “on the run”. Sandwich fixings, anything from the fridge, goes right into the pillows and whenever we’re ready it’s the same temperature as when it was taken from the fridge.

In emergency cooking, I’ve found uses for this as well. One example is a creative yet easy way to re-create a dessert topping. This recipe calls for a can of Thai Kitchen Organic Coconut Milk (I tested three brands and this was the one that worked), and after being chilled it’s easily whipped up into a yummy whipped cream topping. By “chilling” the can using cold water, the can is able to continue to “chill” (until you’re ready to use it for the recipe) by placing it in a Wonder Oven.

Do you have medications which require refrigeration? If the power went out you could use a Wonder Oven pillows to keep these items safe for use as well.

As you can see, there are many uses for this amazing tool. While I keep two sets permanently in my kitchen area for everyday use, in total I have five sets included with our family’s preps. For meal preparations alone (considering we have a large family) as well as keeping water heated for other uses, five Wonder Oven sets is just about right.

Important Items to Remember When Cooking with a Wonder Oven

1. Heat is retained best using thin-metaled pots.

Also, along with the pot, you need a tight fitting lid. Happily, thin metaled cookware is easy to find in stores and is usually some of the cheapest cookware you can find! You can collect what you need at discount stores, even second hand shops. You don’t need to spend a lot on the cookware you need so long as you meet these two requirements.

2. The lid’s temperature, when being put into the Wonder Oven is just as important as everything else.

Once put into the Wonder Oven, the lid and the pot act as a “mini-oven” for your food.  Every surface of the container works to keep the contents of the pot heated.

Most recipes call for somewhere in the range of 10 minutes of cooking time before it’s put into the Wonder Oven . Always remember, during this time, to heat the lid along with the pot.

3. Food never burns and never dries out in a Wonder Oven.

This is one of the things I love most about using this tool. I never have to worry about timing things exactly to keep them from burning or drying out. Very often we’ll begin bread, muffins or steel cut oats in it the night before and when we get up, it’s ready. It’s fantastic!

Can you imagine yourself in a survival setting waking up to warm bread, muffins or hot oatmeal already made? I’d have to think this would be a great morale boost to begin your day.

4. Use the closest sized pot for the amount of food being cooked, aiming to keep the amount of empty air space inside the pot to a minimum.

This one is pretty easy to remember. Empty air space within a cooking pot kills temperature. So, use large pots for larger amounts of food (or when you’re using boiling water itself to cook things and smaller pots for smaller amounts.

One of the biggest “tricks” to Wonder Oven cooking is in finding (and often repurposing) the right sized container for the job. For example, in making muffins, the very best containers I’ve found to use for that job are stainless steel salt and pepper shakers.

In a pinch soup cans also work. Large juice cans (such as V8 or juice containers) can be used for making bread, however because cans have a tendency to rust, my first choice for a more permanent “bread” container is something I discovered along the way: a lidded 3.5 quart Bain Marie pot, found online or in many restaurant supply stores.

Wonder Oven containers

With other recipes I cook using lidded skillets of various sizes for which I’ve found success making lasagna and quiche.

Using a smaller sized and lidded 1.5 quart Bain Marie pot, I’ve had success slow cooking meats. There are lots of options out there – these are just what I’ve found to work for me and what I teach on my site– but the underlying rule overall is to use the right sized container for the job to keep things hot and cooking.

5. No peeking or disturbing the pillows.

To move the pillows around or open the pot “to peek” will surely kill your cooking temperature. That said, there’s no reason why after something is finished cooking it can’t be returned again to the Wonder Oven to be kept warm. Just be aware, depending on it’s temperature, that a “warm” pot may not be warm enough to halt bacteria growth if left for long periods of time.  160 ºF is the magic temperature for food safety.

At the same time, when conserving fuel, previously heated water can always be returned to the Wonder Oven in order to conserve further fuel later, so don’t throw that heated water out!

6. Any “holding” container will work, and sometimes, none at all is needed.

My Wonder Oven pillows are the type which are loosely filled (floppy), usually requiring a container to hold them in order to compress them up against whatever I’m cooking with.

Wonder Oven In Tote

Also, while I appreciate having a lid for the holding container– as it keeps my children from getting into whatever I’m cooking — again, a lid isn’t necessary for it to work.

This point is demonstrated by the following example.

Wonder Oven pillows3

In the case of small things where I don’t necessarily need both of the pillows, such as taking a few items somewhere to keep cool for lunch fixings,  I don’t use a holding container at all.

I simply wrap it all together and pin it shut and it becomes it’s own, lightweight cooler. Going back to the idea of “creating a barrier of beads”, so long as you have just about two inches of compressed beads surrounding your source, heat and cold temps are retained in just the same way as with large amounts of beads.

7. Practice before you have to use them.

Having a set of Wonder Oven with your preps will be most useful (like anything else) if you acquire the technique ahead of an emergency. I’ve enjoyed discovering what can be made with a Wonder Oven and my goal has been to save anyone else who’s interested in learning to use one from having to invest themselves in that same learning curve. Here are many of the recipes I’ve found to work combining long term storable foods while using a Wonder Oven.

For the below mentioned recipes, including step by step instructions and pictures, you can visit me over at Go to the “categories” tab and select “Wonder Oven Cooking”.

Using a Wonder Oven you can:

  • Bake bread
  • Bake muffins
  • Make yogurt
  • Cook rice/grains
  • Make stew
  • Cook small cuts of meat
  • Make “crock pot style” lasagna
  • Make breakfast quiches
  • Make homemade tamales
  • Simmer sauces
  • Make rice pudding
  • Cook steel cut oats and other whole grains
  • …And much more!

DIY – How to Make a Wonder Oven

A pattern can be drawn and measured by following these online directions: Wonder Box Instructions (download).

In addition, because of the fact that so many people have had trouble making the pattern (due to it’s size being large and it’s odd dimensions), I currently offer paper patterns by mail to those who live in the US.  Please remember to include your mailing address.

To sew your Wonder Oven, visit these helpful tutorials:

The Wonder Oven: Works Like a Powerless Crock-Pot
Building a Wonderbox Style Insulated Cooking Box
How to Make a Wonder Oven (Video)

You can purchase the small sized polystyrene beads online by visiting this site. Each bag contains enough beads for five wonder oven sets (so five large pillows and five small pillows):  Foam Factory.

And finally, to purchase a Wonder Oven already made go to:

Food Storage and Survival – Wonder Box Order Page
Prepared In Every Way – Introducing My Wonder Oven

Recipes to Get You Started

Here are some recipes from my website to get you started.  Enjoy!

Coconut Milk Whipped Topping
How to Make Bread in a Wonder Oven
Muffins made in a Wonder Oven
Meat Cooked in a Wonder Oven

Wonder Oven or Wonder Bag?

Whereas Megan provided a good description and a number of resources for Wonder Ovens, I have also heard that the Wonder Bag is a wonderful tool for minimum fuel cooking.  How do they compare?

To be honest, my Wonder Bag arrived a few days ago and I have not had a chance to test it out.  That said, I plan to visit Megan’s website at My Food Storage Cookbook, snag some recipes and get started.  Who said prepping can’t be fun?

Update:  The Wonder Bag is a bust.  I tested it thoroughly and can not and do not recommend it.

The Final Word

Regardless of whether you choose to cook emergency meals on a homemade rocket stove, an open fire, or a Wonder Oven, having a fuel efficient cooking source will be critical in a survival situation.

Wonder Bag Set Up

Setting up my new Wonder Bag

In addition, as with all things preparedness, do not let your cooking source sit idle.  Practice using it (or them) by preparing a variety of food storage items using the smallest amount of fuel possible.

And please, don’t forget to practice your fire-making skills.  You make not need them beyond the initial heating of your Wonder Oven meals, but need them you will!

Enjoy your next adventure through common sense and thoughtful preparation!

If you enjoyed this article, consider voting for me daily at Top Prepper Websites!

In addition, SUBSCRIBE to email updates and receive a free, downloadable copy of my e-book The Emergency Food Buyer’s Guide.

Bargain Bin:  Below you will find links to the items related to today’s article plus some other perennial fire-starting favorites.

Solo Stove:  Having someway to cook outdoors should be a priority.  A rocket stove that burns biomass or wood is a must since propane or other fuels may not be available.  Both of these stoves are easy to use and burn hot and fast.    See Building a DIY Rocket Stove.

Stainless Steel Bain Marie Pot, 2-Quart:  Perfect for using in your Wonder Oven or  Wonder Bag. Also, consider a Bain Marie Pot Cover.  Bain Marie pots Can also be found at many restaurant supply stores.

Survivor Outdoor Fixed Blade Knife with Fire Starter: This knife has measured 7 inches long overall, has a full-tang stainless steel blade, is equipped with thick green cord-wrap handle, and has a nylon sheath plus a magnesium-alloy fire starter.  How does it work?  This is not a Kershaw, Gerber or another high-quality blade.

Swedish Firesteel:  Using this basic pocket fire-starter, you can get a nice fire going under almost any conditions. This is a small, compact version and is my personal favorite.

Magnesium Fire Starter:  This Campers’ Magnesium Emergency Fire Starter.

Coghlan’s Waterproof Matches 10-pack: There are 10 boxes of 40 matches each.  That is a good deal for 400 waterproof matches.

2 Pack Survival Kit Can Opener, Military, P-51 Model:  These can openers makes a great addition to any survival, fishing, hiking, or camping pack. They are lightweight and robust and they just work.

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17 Responses to “Slow Cooking with the Amazing Wonder Oven”

  1. Can anyone tell me if you use the small polystyrene beads or the popped puffs? Also where would you recommend ordering or buying them at a reasonable price I need to make 7 for Christmas presents. Thanks

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