i-adjective
excitable; easily heated up
Describes a person or thing that becomes excited, passionate, or heated quickly. Often used for temperament.
彼は熱しやすい性格だから、議論になるとすぐ声が大きくなる。
He has an excitable personality, so his voice gets loud as soon as a debate starts.
この金属は熱しやすいので、加工が簡単だ。
This metal heats up easily, so it's easy to work with.
熱する is the base verb meaning 'to heat up' or 'to get excited'; 熱しやすい is the adjective form meaning 'prone to heating up/excitement'.
興奮しやすい also means 'easily excited', but 熱しやすい can imply a more passionate or heated temperament, while 興奮しやすい is more about general excitement or agitation.
Compound of 熱し (continuative form of 熱する 'to heat up, to get excited') + やすい (auxiliary adjective meaning 'easy to, prone to').