Fiber tube for 20-35 spark plug wires?

Question for the experts here.  The original "cable tube" (part number E-178) used to hold the spark plug wires on the 20-35 was a "fiber tube" and according to the parts book is 1" O.D. and 2'-1" long.  It is held in place with two "cable tube clips" (part number E-179), which are just simple sheet metal strap brackets that bolt onto the head studs and wrap around the tube.

I have at last one original example of these fiber tubes on my 20-35 from near Minot ND.  Of course it is not in great shape after being in the weather for over 90 years.  So I'm not sure what it is exactly. 

My question is: What are these fiber tubes?  They are not hard rigid, but rather at least semi flexible.  They are not rubber.  And of course not metal of any sort (as many are replaced with in current restorations I have seen).  I am puzzled as to what material these are??

Is there any modern equivalent to what these are/were?  Searching "fiber tube" only brings up a bunch of carbon fiber tube search results.  I'm trying to figure out what I can use for an accurate restoration. 

Thanks!

The next time I am home I'll have to take a closer look at my original tube and get some pictures.  I don't seem to have any good ones handy here.   If you have a couple to post so others can see what we are talking about would be great.

 

I agree that black rubber hose does not look the part.

The Phenolic tube sounds like another possible answer from the quick search I just did to see what it is.  I'll be the first to admit this area of topics is a bit out of my wheelhouse.  But that is how we learn, digging into what we don't know looking for answers.

It sounds like that Phenolic tube may be more of a weather resistant product than the vulcanized fibre?  At least one thing I read on the vulcanized fibre said it was not for outdoor use and would absorb water?  So maybe that is not the answer.  

Robert, from the little digging around on the internet I have been doing, whatever product this tube may be, it probably is some kind of product that can be used in the electrical industry?  It seems that both these products (vulcanized fibre and phenolic) have uses in the electrical world.  Good insulation qualities etc...  So you are probably on the right line of thinking?

It seems that both these products are kind of early substitutes for plastic of the modern day?  Obviously this tractor tube of the 1920's is before plastics were widely used.  I don't believe plastics really became widely used until at least the 1950's, but a quick google search says the plastic was actually invented at the turn of the century, so it was around.

And we all know Allis Chalmers was highly involved in many industries besides tractors.  Ok history buffs, how early was AC into electrical stuff?  Would they have had these kind of electrical tubes and supplies at hand in the 1920's factory?  Just thinking out loud.  Guy at the design office is figuring out what he can use to hold the magneto wires on the tractor they are building.  They want something that is fairly rigid, weather resistant, cheap to have on hand, and resistant to electrical conductivity.  What do we have around?  Go and look in the electrical department, hey, here are some tubes, what are these for?  That will work perfect! 

That is how I see this playing out, but I may be way off.

Either way, it has to be a product that was available in the 1920's.  So that eliminates some plastics and things used today.