Korean chilli is a little different as it has a slight smoky flavour, in addition to being slightly sweet and also quite hot.
The actual name of the chilli use in kimchi and for that matter, most Korean dishes is gochugaru (고추가루).
It comes in a variety of preparations, typically, finely ground, flakes and a paste.
You should be able to find this in most good supermarkets or an Asian store.
If you can't get this, you can still use a good quality chilli powder or possibly, a paste.
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Chili powders are different.
For one thing, the heat they produce can notably effect different areas of the mouth.
Still, they are all chili peppers and many are hot and all are red, when ripe and dry.
Also, there are sweet peppers, like paprika, that are not hot at all, or only very mildly, and these pack quite a flavor punch without heat, so it is not only about heat.
There are many subtle and not so subtle differences.
I made my first Kimchi with mexi-style "California" chili, as they are labeled in this state.
"California" chili is supposed to be mild.
I also add some homegrown dried Fresno chilis and some other ground up hot chilis, which may have been what they label as "Japanese" chilis.
I used a blend.
At first I was disappointed with the flavor, but after the flavors had mingled after 24 and then 48 hours, I found the flavor of my Kimchi very much improved, quite hot, and more than satisfactory.
While personally I would really like to try some authentic Korean chili, if you are interested in making kimchi and can't get a hold of Korean chili or find it difficult, don't let it be and obstacle to making kimchi right now!
Just use whatever you can get your hands on that suits your heat preference.
Season to taste.
I found myself using much less chili than my favorite recipe advised and my kimchi was still well seasoned and quite richly red hot.
Kimchi, cabbage and salt is such a magical enzymatic, probiotic, herbal, medicinal product, that I advise you not to procrastinate but make some right now!
I also emptied a two super probiotic capsules into my kimchi to give it a headstart into lactic acid land and help avoid yeasty pitfalls, as well as make my kimchi more medicinally viable.
But they magic with the cabbage and salt starts really early on in the culturing process.
After just 45 minutes of soaking my washed cabbage in salt it tasted magically enzymatic.
Every stage of kimchi has it's own virtues.
By all means make kimchi with whatever ground chili you can get your hands on!
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The difference may be the conditions the chili grew in.
It's the same pepper, except it grew in a different place.
In each recipe with hot chili, you can exchange it for any other kind of hot pepper, since most hot peppers are almost solely used for hotness and don't have much taste.
You just need to adjust the quantities a bit so it would be as hot as you like it to be.
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For a quick fix in case you can't get gochugaru
I recommend cayenne pepper mixed with sweet paprika powder.
The smoked component is not so strong as to require Spanish smoked paprika, but you may want to try.
Despite what people say: If you are used to Indian, Thai or Caribbean cuisine gochugaru will be rather mild.
It's content in capsaicin is 3000-8000 Scoville Units, thus in the same range than (dried) chipotle chiles.
There is BTW also a type of kimchi that has no gochugaru and is not spicy at all and which is also delicious
, it's called Baek Kimchi ( 백김치 ) Baek Kimchi recipe at Maangchi.com
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Gochugaru is available in Korean/Asian grocery stores, in 1lb or 3 lb bags.
If you live in New York City, it's easy to find.
You can also buy it online, at http://www.hmart.com/ .
Make sure you buy the pure kind, with no added salt or anything else.
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There are quite a difference in chili and korean red pepper have a full rich almost smokey taste besides the heat.
In asian shops you kan find hot or mild gouchugaru and also red pepper powder.
The powder you can use for making paste like gouchuchang or in marinade and sause, not to good in kimchi as you want the chiliflakes to be more coarse when they are sitting for a longer time, kimchi would rest for at least a week
and I let it rest for 2 weeks.
If you use the mild you can have more chili and it adds it color and more of the sweet smokey taste.
The only spice close to korean red pepper would be cayenne pepper.
I tried other chili but they either to hot or not rich enough taste.
You can easily buy korean red pepper flakes from Amazon, they got all three types.
If you don't use much store it cool.
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I've been looking at a number of kim chi recipes and they all call for 'Korean chili powder'.  My visit to the local Asian grocer only yielded 'Asian' chili powder and other nondescript chili powders.  Is there a particular chili powder that is Korean?  Can I simply use cayenne pepper or crushed red pepper flakes?
How does Korean chili powder differ from "US" chili powder?
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<fermentation><chili-peppers><kimchi>
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Most Korean dishes use Gochugaru, which is available in Korean/Asian grocery stores, in 1lb or 3 lb bags. It has a slight smoky and sweet flavour in addition to being quite hot. When substituting, you can use cayenne pepper mixed with sweet paprika powder or any ground chili that is available, and adjust the quantities to taste. Korean chilli used in kimchi is called gochugaru. You can use any other chilli or a mix of cayenne and sweet paprika.
The Korean chilli used in kimchi is gochugaru. You can often find it in Asian stores. It has a slightly smoky flavor. You can also use any chilli powder you find near you or a mix of cayenne papper and sweet paprika powder.