"Head-space, the volume between the liquid and the top of the glass, is a huge factor in creating room for the aroma to aerate. Head-space may not be mentioned often in the average coffee shop, but we coffee-lovers do like to talk about aroma. And the two go hand in hand. Due to the relatively low thermal conductivity of the glass mug, the liquid should maintain a warmer temperature, for the longest amount of time in a ceramic mug. Visit RGMJ Brands Coffee Mug page and checkout our array of custom coffee mugs for all occasions and gift ideas.