A Caldera Cosy

You will have seen the Jetboil and similar devices supposed to save fuel. I suppose they do but there is something wrong with the whole concept of carrying canister stoves. This ‘device’ saves fuel on an alcohol stove.

I have made one for my caldera cone which is an important component of my Cookset but soon to be upgraded my myself to an improved model. My ‘cosy’ will still fit however as I won’t be changing my pot.

I have made this truncated cone ‘cosy’ from a piece of carbon felt (because it is insulating but doesn’t burn) to see  how much fuel would be saved if all the waste heat that escapes out the top of the cone and along the sides of the pot had to be directed into the water in the pot.

It normally takes me 7 mls of alcohol (metho) to bring one cup (250 mls) of water to boiling point (not necessarily boiling). With the cosy cone 5 mls of alcohol not only brought the same cup of water to a boil but kept it boiling for a (approximately) a further one minute.

S0 4 to 4.5 mls of metho would have done what 7 mls normally does, a saving of at least 28% (2mls out of 7), or 35% (2.5 mls out of 7) and maybe  even 42% 3 mls out of 7. More experiments necessary. You can see this is huge. It easily makes up for the ‘alleged’ inefficiency of alcohol as a fuel as compared with gas!

Though this has always been a silly argument because gas canisters and stoves are just so heavy (especially for short trips). For a ‘normal’ weekend trip using an alcohol stove has to save you  carrying at least a couple of hundred grams.

The cosy in its present form weighs 18 grams (a little over two cups of coffee worth of fuel) but I imagine it can be squeezed down a bit. I made it 2 1/2″ high and of fairly thick felt, and my design and joining of the fabric can also be improved.

In a thinner fabric at maybe 2″ high and with less wastage in the join it could easily come down to 10-12 grams. Well worth carrying for the fuel saved. I also need to work ot a better way of joining the fabric (a fireproof thread for my sewing machine would be the best option).

Here is how I made it:

I marked out the curve  2 1/2: in on the inside of the cone and made a pattern out of a piece of oven paper. I needed to extend the curve a couple of inches. I had to make it in two pieces because the carbon felt I could readily buy came in 8″ x 12′ ( 20 x 30 cm). Two pieces cost me less than A$20 on Ebay delivered.

I tried hand sewing the pieces together with some carbon ‘tow’ (thread) I had from another project. This did not work well for me due to finger arthritis. I think rivets or press-studs would work fine (especially if you could juts make it up with one longer piece of carbon felt. I ended up joining the pieces together with a paper stapler (which worked) but it is not a permanently satisfactory solution.

I only used (part of) one. There is plenty still for other interesting projects. It would make a good ‘handle’ for an ‘ultralight’ plastic coffee cup for example, or as an ultralight pot lifter & etc. I will find other uses. You could also use some as a floor to put under your Hobo Stove to stop it burning the ground.

PS: There really is fire-proof  or flame retardant thread such as aramid. You can buy a reel from Aliexpress for less than $5. It will take a while to come so I will complete the project when it does.

PS: The finished project can be found here: Mastery of Fire.

See Also:

DIY $4 & 20 Gram Roll-Up Titanium Stove

Mastery of Fire

Cookset Solutions