They're the first on-ear headphones I've owned. I think I've generally kept away from them, worrying about comfort – I imagined that anything that sat on my ears would only be sufficiently comfortable if they were luxuriously microfibred or something, and relaxation is one of my main goals when favouring headphones over speakers at home. I find EarPods comfortable, and until I bought these Beats Solo 2 Wirelesses, I'd used Sennheiser over-ears, which are very lightweight and fluffy.
It's hard to answer the heat question – it's not something that's ever bothered me so far, and I live in an area that's occasionally hot, but often cool or cold.
Knowing all that – generally comfortable: yes, I find them comfortable – one of the reasons I came to love them. They're not like velvet sheets, but the cups are a slightly rubbery, leathery material; almost like an imitation animal skin. There's a certain amount of plushness and give beneath that surface. It conforms and seals well, eliminating the majority of external noise. If there's any sense in which they're uncomfortable, it's that the sensation nominal pressure accumulates over a period of over an hour or more, and that's just me.
