We use an alcohol stove with a Caldera Cone from Trail Designs https://www.traildesigns.com/products/caldera-cone-system. However, it is our DIY thermal mugs that only weigh 2.9 oz. that really conserve the fuel by cooking efficiently with boiling water and keeping the food warm for a long period of time as we relax and eat. We find they are very efficient for true thermos cooking. The same would be true if we used other types of stoves as well.
I have read a number of references to thermos cooking on forum discussions and it is simply very efficient “cozy” cooking but I will regress a little for those who are not very familiar with it. We used to avoid all foods that required any amount of simmering or cooking time (say 15-45 minutes) and only took “instant” (5 minutes or less) cooking time foods. We would put them in our old thermal mugs and let them sit for longer periods of time until they were sufficiently cooked and thereby again minimized our cooking time where fuel was being used. However, we now have very efficient thermoses that are very light weight and use foods that call for up to 45 minutes of simmer cooking. It of course takes longer in the thermos compared to keeping it over the stove but we start the meal and let it sit in the thermos while doing other camp chores and then relax to a very hot and delicious meal.
Thermos construction. We are aware that many today use Reflectix but we know the slightly heavier closed cell foam is far superior in R-value, can create a better seal and is worth the little extra weight.
We started with the powdered Countrytime lemonade containers that have the tapered pour spouts inside the screw top. You start by cutting the spout off, carefully leaving the rolled lip at the top of the threads so you are not putting your mouth on a sharp edge when drinking from it. This is not a new idea as we gleaned this from a light weight backpacking site several years ago. Next we take a permanent marker and put a one cup mark inside the main cup and a half cup mark inside the lid (which doubles as a sipping cup sometimes). Next we made snug thick cozies from ½” closed cell foam (an exercise mat https://www.amazon.com/gp/product/B01LW97F6T/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 This particular one is very firm so it holds it shape well and is black so it doesn’t show coffee stains, etc. Y don’t bring the sides up all the way as the insulation will be right where you lips go when drinking from it (morning coffee).
Cut 4 pieces of foam: a piece 3” x 14 7/8”; 2”x14 7/8” and 2 disks 4 5/8” in diameter. I marked the dimensions out very carefully with a ball point pen and found kitchen scissors easily cut the material though the round disk had to be cut it short strokes as the scissors mash the foam as it cuts so it can be hard to follow your lines. You will assemble with a hot glue gun which can not only be messy but you can easily burn yourself while fitting pieces together (ask me how I know!). Take a couple of rubber bands to hold the strips in a circle (you have to experiment to find ones that don’t crimp it too tight but hold the two ends firmly together so it forms a nice round circle. I then put a thin piece of plastic on the outside at the joint (under the rubber bands) so that any seeping glue would not stick to the rubber bands. I then pushed the butting ends inward slightly to expose them and reached inside the circle with the glue gun to spread a thick bead of glue, pushed it back into the circle and then let it cool completely. Do the same thing for the 1 ½” strip. If you have a lot of excess glue you can both peel and/or cut it off. You are better off having excess glue to clean up than not having a full bond where the joints may later tear loose.
Check the fit but if you make the strips exactly 14 7/8”, the container and the lid should fit in snugly. Next you want to glue the disks on each of the circular pieces. Since the glue is messy and hot and you need some pressure, do the following: cover the lid and the container with plastic food wrap and then slide them into the circular pieces. Run a bead of glue around the perimeter of the disk and mate it to the side wall pieces. Some glue should squeeze out and use a slight weight to hold them firmly in place until it cools. You can then trim off excess glue on the outside with the scissors. If any excess squeezed inside, the plastic wrap will have kept it from sticking to your container.
You will now find it difficult to remove the container as it forms a suction (the lid will not be a problem as it is much shorter). Once you get the insulator off of the container, use a small knife blade cut a triangle hole in the bottom and you will find it can be removed much easier.
We also made nylon strap handles similar to what you see on the Jetboil and glued them in a loop with a short supporting piece at the top so the handle doesn’t pull away and the cup sag when the cup is full (heavy). The exercise mat comes with a nylon strap handle and that is what we used. The top insulator is long enough to extend down and contact the side insulation when the lid is screwed on. With the lid screwed on, the two cozy pieces mate making a very well sealed and efficient thermos that weighs only 2.9 oz. with the cup. Even with foam that is ½” thick (much more than most) these are pretty light weight, easy to hold with the strap and a thick, tight fitting cozy makes them perform nearly as well as a commercial thermos bottle. We use them for eating mugs, holding the cozy top between two fingers, setting it on top between mouthfuls and we find our food stays very hot to the last bite.
Some would say using only the titanium pot for what you both cook and eat in weighs less but we think we save enough fuel to make up the weight and our coffee and dinners stay hot for a very long time. If you are traveling solo you could have a cozy for the pot but the lemonade container weighs almost nothing and getting a snug fitting cozy on a hot pot is sometimes difficult (we know–we did that for a long time).
For a performance test we put 1 cup of boiling water in and it was still 165 degrees after 20 minutes (too hot to eat).
One variation is when we use the thermos lid for a drinking container with our meal in the thermos. We slip the cozy off of the lid when we are ready to eat, still using it between bites to cover and keep the food hot, but the lid is just the right size for a small drinking cup. We also use a disposable cup from Southwest Airlines as a main drinking cup as it fits right in the lid of the container.
