Quantitative assessment of pleasant touch.
-- GK Essick et. al., Neurosci Biobehav Rev 34(2):192-203 (2010)

The hedonic attributes of tactile stimulation are important to one's quality of life, yet they have rarely been studied scientifically. The earliest experimental investigations suggested soft and smooth materials as pleasant, those that were stiff, rough, or coarse as unpleasant.