This is a huge pet peeve of mine with many of the airlines (especially Asian ones). The cabins are way too hot!
I have never understood, why they are insisting to keep the cabin temperature at 24 Celsius or more that makes flying uncomfortably hot. I usually ask to speak with a purser and request them to lower it to 21 Celsius or so.
Again, I encountered this past Friday, when I took JAL’s flight from DME to NRT. A few minutes into the flight and I was already uncomfortably hot. I spoke with the purser and requested her to lower the temperature to 21 to 22 Celsius. She said that she would like to keep it at 23 to 24.
She came back few minutes later and told me that they had forgotten and left it at 26 Celsius. No wonder why it was so uncomfortably warm.
If you feel that the cabin is too hot, just press the flight attendant call button and request temperature to be lowered. I am always more comfortable in a cabin that is around 20 Celsius than 25+.
On a side note, it never ceases to amaze me how little some FA’s understand English. I asked one of the attendants, while still being on a ground, if they had heated up the batteries (this was 787) and she said that she speaks very little English.