Printed Hand Warmers, questions answered.

Printed hand warmers have been made here at Thermopacks since the early 1980’s. Having manufactured close to a million reusable hand warmers over that time, for hundreds of different companies and organisations; we’ve noticed the same questions being asked. This blog piece answers all your questions about the finest printed hand warmers known to man.

printed hand warmer
printed hand warmer

How do reusable hand warmers work?

It may come as a surprise, but salt is the active ingredient in our printed hand warmers. To be more precise, we use Sodium Acetate – and add it to warm water. When added to warm water, the two parts of the salt crystal, sodium and acetate, break apart. What’s left is a solution filled with suspended broken particles, just itching to get back together.

Whenever a chemical reaction occurs, (like breaking apart the salt particles in a promotional hand warmer) energy is involved. We need to use heat energy to break the particles apart, and it doesn’t just disappear! Now it’s time for the metal activator disc to kick start a process known as an exothermic reaction.

The snap of the activator disc causes a spark of energy to hit the solution. That spark causes the two particles, sodium and acetate, to collide back together. You’ll see the solution change as all the salt particles re-crystalise, and as that process takes place, it generates that beautiful heat. It’s not rocket science, just science.

How do you activate hand warmers?

Our reusable hand warmers are activated using a metal disc. The metal disc is floating within the solution. By firmly flexing the disc, a small spark is created, and it’s that spark which causes the pack to crystalise and in doing so, causes the hand warmer to heat up.

activator Disc

The solution within the hand warmer is sensitive. If you drop the hand warmer or even give it a vigorous shake, that can sometimes be enough to set-off the reaction.

How do you add logos and design to the branded hand warmers?

We manufacture printed hand warmers to order. That means we start with raw materials and convert those materials into the final product. Some suppliers print on the top of a product that’s been manufactured over seas. We don’t! Our process is to cut panels of materials and print onto those panels, which then are manufactured into printed hand warmers.

printed hand warmers
screen printed hand warmers

We use two printing methods to do this; screen printing and digital printing. Screen printing is where ink is run through a stencil and onto the material. You may have seen images of T-shirts being printed this way. Screen printing is a great method to get specific colours onto the promotional hand warmer, known as Pantone colours.

Digital printing is essentially the same as your printer at home – only a much bigger version. The digital printer uses a mix of cyan, magenta, yellow and black inks to produce full colour artwork. Hence the terms CMYK, the K standing for black.

printed hand warmers
full colour printed hand warmers

Because we print flat sheets, our printed hand warmers have a larger print area than hand warmers where print is added after the product is made. That keeps logos and messages nice and big, easily recognised by your customers.

Can we have the solution is different colours?

Yes you can! Bespoke hand warmer manufacturing means that you can choose the colour of the solution used. We use 100% non-toxic food dyes to colour the hand warmer solution. The colours available are all pastel shades of yellow, red and blue. Whilst we cannot Pantone match the colours, we can control the strength of colour to a certain extent.

Are hand warmers dangerous?

No, not in the slightest. Our promotional hand warmers and retail hand warmers are manufactured here in our Dorset factory using fully compliant materials. The vinyl is Phthalate-free, and as detailed above, the solution is simply a combination of salt and water. 100% non-toxic product guaranteed.

The hand warmers heat up to a maximum of 53-degree centigrade, and immediately start to cool over a 20-30 minute period. First degree burns (such as sunburn for example) occur at approx—65-degree centigrade, with plenty of pain warning before that. So, whilst not for babies and toddlers, hand warmers are perfectly safe for everyone else.

How do you make hand warmers work again?

Our branded hand warmers are easy to re-charge. It is much like cooking pasta or boiling an egg. Fill a pan with enough water to cover the hand warmer, 2 pints / 1ltr is plenty. Bring that water to the boil and turn down to a simmer, and then place the hand warmer into the water for 10-12 minutes.

You’ll know when it’s ready to take out because the crystallised and hard hand warmer will have turned back into the clear liquid. Carefully remove the hand warmers from the water, and allow the hand warmer to completely cool before using again. This process can be repeated hundreds of times, with no decline in the hand warmers performance.

printed hand warmers
round printed hand warmer


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