Works "o.k.".  My pump (avent isis iq duo) has plastic that covers the horns.  The plastic tends to lose connection, so I still have to sort of lean against something to keep these in place tightly, but I don't have to use my hands to hold them, but I lean the whole time against a table.  Also zipping it up can be a trick (I am big busted, particularly full of milk) so that could be why.  It is highly adjustable for sizing.  The material is high quiality.  Doesn't work as well as I was hoping, but it does help.