Vibration may lead to premature receiver or battery failure. Isolating these components with a foam wrap is how savvy modelers protect them (and against impact damage due to a crash). Achieving said protection for your receivers and batteries is remarkably easy and involves common sense. Simply wrap each in a piece of foam and presto, you're done! But all foam isn't equal.
These are manufactured of a black synthetic polymer foam (neoprene, but specifically ethylene-propylene-diene-monomer - EPDM). Its principal advantage over the ordinary 1/2" white latex-foam hobby dealers offer for the same purpose, is the neoprene doesn't quickly deteriorate and crumble due to ozone.
Yes, it costs a bit more (principally due to the nifty Velcro D-ring strap versus #64 rubber bands that get hard and fail over time). Against the slight added expense, I've got models with receivers wrapped in this stuff since 2010 (yes, over a decade). The neoprene remains soft and pliable whilst maintaining perfect integrity and resilience.