The Eibach ERS spring rubber, durometer 90 in blue, is a rubber spring isolator made to sit between coil wraps or between spring and seat to cushion contact and help damp vibration. Sold as a purpose-specific replacement component, it’s used where correct rubber durometer and fit are required to reduce noise and preserve spring seating during normal use and service.
Eibach Spring Rubber - Durometer 90 (Blue)