When did black conductive anti-static foam stop being conductive?

[PhotonWrangler]

Tonight I ran across a good sized chunk of what looked and felt like black conductive anti-static foam, the stuff that's impregnated with carbon. I wanted to confirm whether it was the real thing so I pulled out my VOM, put it on a high resistance range, stuck the probes into the foam, and... nothing. So I located a nearby integrated circuit that was sitting in a little rectangle of what was supposed to be conductive foam, put the VOM probes on it, and... nothing again.

I distinctly remember that I used to be able to get a fairly low resistance reading when measuring across that crunchy black foam. Now I'm starting to doubt whether most of my anti-static chip storage foam is real.

 

[louie]

I wonder if you need a low DC resistance for static safety? What happens if you use probes on a static-safe plastic bag?

Rapidly looking at a random spec sheet for static dissipative foam, I see a spec for surface resistance of 10E3.

I suppose it's also possible some products did have a low DC resistance.

 

[bykfixer]

Ok call me crazy but wouldn't the name anti-static imply that it's non conductive?

 

[PhotonWrangler]

Ok call me crazy but wouldn't the name anti-static imply that it's non conductive?

Not a crazy question at all. The conductive material shunts out the static buildup. It's the same reason why you get more static buildup in your hair from a plastic comb than a metal one.

 

[Dave_H]

Two basic types of foam: pink (usually) polyethylene which is anti-static but not conductive, and the black stuff which is conductive. I picked up a piece of the latter which has been around for awhile (decades) and it crumbled, so it must dry out or otherwise break down (made a mess).

I checked two small pieces of 1/4" black foam, old but still pliable, with ohmmeter. Both showed 10k-15k ohms with probes about 1" apart, which seems OK.

Dave

 

[PhotonWrangler]

Two basic types of foam: pink (usually) polyethylene which is anti-static but not conductive, and the black stuff which is conductive. I picked up a piece of the latter which has been around for awhile (decades) and it crumbled, so it must dry out or otherwise break down (made a mess).

I checked two small pieces of 1/4" black foam, old but still pliable, with ohmmeter. Both showed 10k-15k ohms with probes about 1" apart, which seems OK.

Dave

Thanks Dave. Yes, the old carbon foam did have a tendency to crumble and make a bit of a mess. Maybe there was a change in it's composition because of this, trading off conductivity for mechanical stability. All of my recent purchases of thru-hole chips come in anti-static plastic tubes so I don't have many samples of foam to compare against.

 

[Monocrom]

Plenty of companies will quietly tweak an existing product, but not mention it to the Public. Wondering if that was the case here.