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The wonders of Kairo – Japanese heat packs

Kairo - Japanese heat pads

I first heard about the magic of kairo when we were preparing to go to Japan for the Sapporo snow festival.  I live in the sub-tropics and I really don’t like to be cold so I was wondering how people went about day to day life when it snows every day and the temperature has a minus in front of it.

When you’ve always lived in a temperate or sub-tropical climate it can be hard to imagine what extremes of cold feel like other than the cold room at the local bottle store.  I’m sure that goes the other way round too for those living in cold climates and travelling to tropical islands or the desert.

Hiking in Nagano

In reality I loved spending time in Sapporo in winter, hiking in the snow through a National Park in Nagano and a whole range of other snow based activities while in Japan.  It was wonderfully different to anything I’d experienced before and to play in fresh powder show was a lot of fun even as an adult.  I would absolutely rush back to Japan in winter time as soon as I get another chance.  That said, the tip I received about kairo was a good one and not something I’d heard of before so I thought I’d share.

So what are Kairo and how do I use them?

Kairo are a single use heat pack that you activate when you are ready to use it and they stay hot for at least 8 hours, some brands up to 15 hours.   You pop them into your pockets to keep your hands warm or attach them to your clothing such as an under shirt to provide heat around the body core and lumbar area.  They are extremely toasty and comfortable to use.

As far as I can tell the extensive use of this form of heating pad to keep warm is fairly unique to Japan but I can see they might be useful for any cold weather sports or activities and also be beneficial for arthritis or other injuries where applying heat can be helpful.  Japan doesn’t use central heating to the degree that many western countries do and both walking and use of public transport is the norm so people spend significantly more time outside.

There are a few key differences between kairo and the more common heat packs we use in the west such as wheat bags, hot water bottles and the crystal click heat packs.  The first is that they can be easily transported and activated when needed without other equipment.  When in use they are thin and discrete, fitting unobtrusively inside your clothing and once attached in place they mold to the body and don’t move around or need adjusting.  Kairo also stay hot for a much longer time than other options.

Snow in Sapporo

Kairo usually come in bulk packs, the ones we got were in packs of 10 and they are individually sealed inside.  When you are ready to use one you remove the plastic cover and the pad will activate when exposed to the air.  I believe an older type required a bit of a vigorous shake and some people still seem to do that out of habit but it’s not required.  Then pop it in your pocket or remove the adhesive backing and attach it to the clothing with the adhesive side facing in towards you.  Don’t attach it directly in contact with skin because they do get quite hot, somewhere between 40 -65 degrees Celsius.

How do kairo work?  Is it safe?

The kairo package contains iron filings, water, vermiculite, carbon and salt.  When exposed to air the iron oxidises and heats up over a period of about 10 minutes, it then stays hot for around 12 hours.  Only open the packet when you are ready to use it.  I haven’t tested it but was told you can stop the oxidisation (and heat) by placing it inside a sealed plastic bag if you are quick.

All the ingredients in kairo are natural, non toxic and safe provided you use as directed.  In Japanese homes where getting rid of your rubbish is a complex process with a lot of sorting required, the used packets are often emptied into the garden and only the paper sachet put in the recycling.

As with most products there are a few warnings around their safe use.  If you have reduced skin sensitivity,some people with diabetes experience this, you shouldn’t use the pads as you may not realise it is too hot in contact with your skin, likewise you shouldn’t really sleep in them (yes, do as I say not as I do) and don’t use them on infants or when pregnant.

The sticky side goes onto your clothes not directly on your skin, this avoids any issue of skin allergies or reactions to the adhesive.  They are best used on a thin layer of fitted clothing such as a singlet top so they stay firmly in place and you get the maximum warth.

Where do I buy them?

In Sapporo these were for sale pretty much everywhere, pharmacies, discount stores and train stations were easy places to find them as they were prominently placed.  I imagine the snow festival was an optimal sales time for them.  We subsequently found them in stores all around Japan, mostly things like the 100 yen stores (eg Daiso), sometimes in the corner stores like 7-eleven and regularly in the discount pharmacies that have the big racks and bins of products drawing you in.  In winter if you’re obviously foreign and ask for something that sounds anything like ‘kairo’ I’m sure they’ll be able to help you.

Central Sapporo streets

Recently I’ve been looking for these in Australia and they are pretty hard to source in stores.  I have a form of arthritis that causes intermittent pain in various joints and heat is a big help in achieving comfort without increased medication.  I’ve found that Daiso internationally do stock kairo but the brand in Queensland has some issues with not heating up enough.  I’ve tried two different sizes from two stores and while Daiso staff are good and they have a fair replacement policy they don’t really seem interested in looking into the issue.  Having said that I’m told the ones sold in Daiso Victoria which are under different store ownership work fine,  just like the ones in Japan.

You can also buy a similar product under the brand Hotteeze from a few physio’s and online, they sell at a higher price working out around $2.50 per use but honestly, I really am finding they’re worth it and they do last over 12 hours.  These are the ones they stock in Amazon Australia, the packaging generally looks very similar to this despite there being many brands available.

With winter settled into the southern states and the Australian and New Zealand ski season underway I’m sure there would be many uses for these within Australia as well as on our travels.

If you’ve given kairo or a local version of the disposable heat packs a try let me know what you thought.  If you’ve found a good and reasonably priced supply outside Japan even better!


  • i also found when I bought the hot packs overseas then brought them home, they were not as effective. also i’ve found issues with Daiso hot packs bought outside Japan. they did not work at all when i was going to use them. glad to know that the one sold in japan and used directly works their magic coz i’m going there this February

    I have concern with the sticky type though. are they safe for soft fabrics? i’m afraid when we pull them ,it’d also pull out the fabric or some of the fabric stick on it

    • Hi Jen, I have used them more frequently outside Japan now and found some work well, if it’s not really cold and you’re using them for aches and pains they don’t feel warm to the hand but they do infuse their heat into the area they are in contact with and give long-lasting relief. In the colder parts of Japan in winter I’ve worn them on my underlayer, usually a very fine marino wool camisole or delicate heat-tec fabrics and they haven’t done any harm on either of those, no sticky residue or pulls / stretching of the fabric.

  • It would have been awesome if you included what the kairo heat pack is made of (like the chemistry) but I enjoyed this article.

    • Hi, thanks for your question. As explained in the article “The kairo package contains iron filings, water, vermiculite, carbon and salt. When exposed to air the iron oxidises and heats up over a period of about 10 minutes, it then stays hot for around 12 hours.” I’m not a chemist and I would expect with the variety of these now on the market in different countries the combinations would vary a bit between products but this is the basis of the reaction that generates the lasting heat in the ones I’ve used.

  • I also live in the subtropics – I took the Hoteeze brand to Japan in 2015 when I visited in November . They worked a treat! I didn’t realise you could buy something similar in Japan. (Silly me – what can’t you buy there!?)

  • Yes! I love these. In Japan they’re so plentiful and I couldn’t find them at all when I came back to Oz. But now in Daiso (Victoria) they do have them and they are the good ones! Two sizes, smaller and bigger (bigger is better) and they have the stick on type and nonstick type. The brand kinda changes per year but they sell them in packs of 5 for $2.80 (which seems a rip off compared to the japanese ones x10 packs! ) But yeah. Totally worth it!

    • Yeah we’ve just been down to Melbourne and I totally forgot to duck in and pick up a couple of packs for this winter – hope to grab up some more in Japan later in the year – or have heard rumours Australia is getting it’s own Amazon too soon.

  • Hi,

    We tried the heat packs when we were in Japan during the winter and it was heaven. I live in a tropical country (Philippines) and not used to cold weather. I read about it when I was doing my research before going to Japan so I was prepared. I used both the one with adhesives and 1 without. It saved my fingers from freezing 🙂
    I brought a couple of packs home to give as gifts to my family and friends. Unfortunately, it didn’t work as well as when I used it in Japan. Not sure if its because its hot in the Philippines? or its not meant to work that much if its not cold? I’m certain the ones I brought home were new batches so not really sure what happened. I was hoping to see my friends reaction when we try to open one up and feel it getting hot 🙂

    • I guess it will naturally feel hotter if you use it when you’re really cold. I have used a version in winter in Queensland for arthritis and even though it’s not that cold here it did work for warming and relieving discomfort. It definitely didn’t feel toasty warm like it does in the snow although for my use I was pleased it didn’t or it would be uncomfortably hot in our climate so maybe it is relative to the ambient temperature. Interesting.

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