110ºF are 43,33ºC. The "accuracy" required is not that high, however, when they say "hand warm temperature", so they should have written "about 110ºC.

It seems they will not actually use any thermometer, either, so I would say (to cover all bases):

""unos 40ºC [entre 40 y 45ºC], es decir, a temperatura que se perciba cálida, pero no perjudicial, al tacto"

And sorry if the Spanish phrase is quite longer.

Si es tibio es redundante usar la palabra temperatura.