Warm yes. Uncomfortably hot, no.
edit: after many tin foil prototypes I've managed to make a pretty awesomely preforming design for a bowl cap.
It is a long ridge of foil like this /\------\ with a pinhole in the centre. the foil is folded over several times for added thickness. I've managed to get a number of consistently good clouds with this and a .2
. Doesnt seem to affect flavor much, and I dont mind using aluminum, others may have concerns, but vaping is still in the safe cooking temperature zone for foil. The taste is also unaffected by the foil imo, so I dont mind. This design is really preforming well.