I bought some Tinder Cards to try. Here's what I found.
They are quite thick - equivalent to between 2 and 3 credit cards. They are also quite large, each card measuring a little over 3.5x7.5". Of course you can cut them down to whatever size you want. A small strip 1 inch by half an inch burns for about a minute, a 1" square for a minute and a half. You get 6 cards in a pack. Overall it seems like a lot for the ?2, potentially 300 fires. (The cards are scored to be broken in 3, which is why the advert says 18 strips with a narrower width.)
They are dry and slightly waxy. A Fisher Space Pen will write on them; a lesser pen won't. Their texture is layered, different to the more uniform compressed-cotton texture of Spark-Lite's Tinder-Quik. They burn to leave a solid residue with embers that glow red for quite a while. Extinguish with care.
It took me a little experimentation before I could light one with a flint rod. First you have to spread the layers, then you have to rub it with your striker to rough up some fluff, then a spark will ignite the fluff and the spreaded part will catch too. It has to be very light fluff. Tinder-Quik is much easier, less fiddly and more certain to work first time. If you already have a flame, eg a lighter, then the Tinder Card catches easily and you don't need to bother with the spreading/fluffing.
They are not advertised as waterproof and they aren't. I held one down in a glass of water for 20 minutes, and when I fished it out it was soaked through. There was no dry bit in the middle like there would be with Tinder-Quik. When wet it doesn't burn. I could just make it catch with a lighter, but then it would likely go out. I tried dunking one for just a few seconds, and it did survive that, but if you had one in your pocket when you fell in the river, you wouldn't be able to rely on lighting it when you got out. <img src="/images/graemlins/frown.gif" alt="" />
Over-all, I see two advantages over Tinder-Quik: they are much cheaper, and they have a different form-factor. They are drier than vasaline-soaked cotton-wool.
I currently expect to use them for casual fire-lighting when camping. I use Nesbit-style stoves, and find the hex fuel blocks hard to get going with just a lighter. I had started using Tinder-Quik, but although I have lots of it (50 piece bags) I was concerned that I was using it up. I am pleased to have an alternative.
The lack of water-proofing means they cannot substitute for Quik-Tinder in a survival kit. And frankly I'd rather have two QT then a QT and a TC, even if the Tinder Card is kept dry. However, they may be worth including in places which don't suit the Quik-Tinder form-factor. Quik-Tinder has a certain irreducible thickness - if you cut it to make it thin it stops being water-proof. I am going to carry a Tinder Card in my wallet. Unfortunately they are much too thick to go into the battery compartment of my phone. I will see what other places I can find.
I am currently undecided about whether I can remove anything from my EDC as a result of adding the Tinder Card. At the moment I have a keyring spy-capsule with the spark mechanism from a lighter, which is a bit lame, and 2 QTs. I don't carry a flint rod. Ideally I'd like to omit the spy-capsule, add a flint rod (I have a nice one ready) and add a TC in my wallet. But I'm not sure. It's such a shame they aren't waterproof.
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Quality is addictive.