The black foam ESD protection material is a carbon loaded foamed polymer with a relatively high bulk conductive value. It also has the property of degrading into a crumbly mess over time, giving off some sort of corrosive product. I lined some plastic drawers with the black packaging material around ten years ago and stored most of my mos transistors, cmos and memory chips in the drawers. I found sometime recently that some of the least used devices stored in the foam had started to show signs of corrosion and adhesion to the foam on the pins. Maybe a reaction with atmospheric moisture or materials in the foam causes this. Devices stored from much earlier in the plastic shipping tubes show no such deterioration.