Why are wet slippers slippery and grippy at the same time? Wet slippers are slippery on some surfaces and extremely grippy on others. Why is it so?


I believe the answer lies in the way water interacts with the two surfaces.
But how can this interaction give rise to such contrasting effects on different surfaces?
 A: There are several factors at play here:
1.The tread pattern of given slippers
 2.The surface roughness (i.e, the unevenness of given given surface)
 3.The coefficient of friction between surface and the slippers.
To put in perspective it is obvious that more the coefficient of friction between surfaces, less the slipperiness. Unevenness of the surface relates as, if we increase it from smooth to rough the slipperiness first decreases and then increases (my guess is with extreme smoothness the treads create some sort of suction and as smoothness decreases this suction reduces and later on more roughness leads to the increase in contact area for normal friction to act). Also tread patterns play a vital role in determining slipperiness as different patterns of different heights provide different conditions of areas of contact and different amounts of liquid displacement in the case that liquid (here water) is present on surface. 
 Liquid on surface reduces the friction due to fact that it slides on the surface, more viscous the surface, more the time to slide resulting in greater chance of slipping. 
NOTE: I have sourced this from the following reference https://www.kgk-rubberpoint.de/wp-content/uploads/migrated/paid_content/artikel/1507.pdf.     
