What is the plastic for?

[yotter]

In the doors of my Tranny underneath the standard hardboard panels there is a transparent blue sheet of plastic stuck down all round. What is the purpose of this? I do intend to insulate the doors but do I need to reinstate the plastic sheet afterwards?

[Brains_transit]

It's a moisture barrier, personally I would reinstate it but clear rubble bags can be cut down and used with a spray glue to reattach

[d.e.hill]

You definately need this plastic for a conversion.

As said above, it's a moisture barrier that performs a range of functions. As you breath out warm moist air while sleeping, this can condense on the cold metal sides of the van causing:

- rust in the panels
- damp and subsequent rot of wood
- soaking of insulation (rendering it fairly ineffective)
- interior drips

The moisture barrier stops all this.

The best policy is to insulate directly against the van skin. It's about a 50mm cavity. You can check out my conversion thread to see how I did it. Then stick over the barrier. As stated, rubble bags works, but I used a big sheet of polythene from a DIY store and some PU sealant (silkoflex).