From emails 2013:
http://www.mcmaster.com/#__catalog/119/3431/=nt0hh8
But there were some concerns that the tape is not designed for the weight
of the door and that it wear through fairly fast.

Karl.

On Wed, Jun 6, 2018 at 7:45 PM David Beierl <dbeierl@attglobal.net> wrote:

> I strongly suspect the tape is HDPE (High Density PolyEthylene).  Widely
> used as low friction surface in woodworking.  But seriously -- yours is the
> quietest slider I have ever heard on a Vanagon.  Why are you obsessing over
> this?
>
> You have the new-type door.  It is significantly different and better than
> the old type.  If you want it quieter than it is, get a set of the Delrin
> rollers made by ?Mark Garnick? and sold by I think Van Cafe and maybe GW.
>
> :)
> d
>