Adding my thoughts as someone who cannot sleep in a hot cabin. I just got back from 4 legs on JAL- to/from the US to HND, and to/from HND to DEL. I went prepared for a wam cabin, with a t-shirt under my regular shirt so I could strip down as needed. On the 2 US flights, cabin temperature was nearly perfect for me-- slighly cool such that I could sleep well with a long sleeve shirt and the duvet (cardigans were offered on the flight from HND and many Japanese passengers took them, but I found it very comfortable without). The flights to/from DEL were very hot, even wearing just the t-shirt and putting the duvet in the overhead bin. I did request they lower the temp on one flight, and that helped a little, but the second flight stayed hot throughout, and I was wishing I had been clever enough to bring a USB fan as suggested by JSSAUCE.