Actually, while you're saying you're in Europe and have linked to the TSA Blog, the answer is actually there, if you read between the lines:
Crystallization – This is the type that you flex or squeeze to
activate. They contain liquid and require adherence to our 3-1-1
guidelines. They can be packed in both carry-on and checked baggage.
SO the key thing here is that they contain liquid. Naturally, this means they're subject to any airline regulation regarding liquid.
From the European regulations:
Liquids carried in the aircraft cabin such as drinks, toothpaste,
cosmetic creams or gels must be carried in a transparent plastic bag -
maximum capacity 1 litre - and no container may hold more than 100 ml.
Liquid containers larger than 100 ml must be placed in checked
baggage. The volume restriction does not apply to medicines and baby
So your best bet is probably to put them in a clear bag like every other liquid you have, and when/ if questioned, explain there's a small a mount of liquid in the gloves. To me it's less than 100ml (I've used them before) but they may want proof, in which case you may want to find the spec sheets for your specific gloves to bring along to show that it's merely 40ml or whatever.
If you can show that, then by law, you meet the legal requirements, and you'll be permitted aboard with them. The spec sheets will also show that it contains merely sodium acetate (like baking soda and vinegar), but it's the ml that will convince them, I suspect.
You may still get someone who still doesn't trust them, in which case you may have to lose them or check them in the hold, so get there in time and allow for this.