An ideal temperature for a warmed towel is around 110F to 120F.  This is slightly warmer than your skin temperature when you emerge from a shower.  This ensures a comfortable transition from 100F (the water temperature which your skin equalizes with) to a 70F room whilst you are drying.
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Please note, by design the towel will not feel hot to the touch (like it would directly from a dryer) especially when you are dressed and dry. The aim is to remain comfortable and relaxed.  Whilst a hot towel is pleasant, it increases thermal shock when removed.  A warm towel maintains your comfort.