Carpet backing, carpet Options

[Medtner3]

just recently got my 10 piece carpet set from 914Rubber it is beautiful

However, there's no backing to the carpet and the original had a sort of clear plastic perhaps the same material that is inside the door panels

Would anyone have any recommendations as to what would be a good backing for the carpet?

[wonkipop]

I don't recall any plastic on the back of my old stock carpets, but It's been awhile and they are long gone.

The plastic sheeting behind the door cards is a vapor barrier, which wouldn't be needed on the carpets. You should be able to lay them down 'as is', using the grommets to hold the main floor pieces in place. It may take some time for the all of the pieces to lay down fully and conform to the shape of what they are covering.
I didn't need to, but some recommend using a light adhesive spray to hold things in place, especially for the pieces that go over the longs.

the original factory carpets had a variety of backings depending on the position in the car.

the pieces that were heat formed to shape had what you might describe as a kind of clear plastic layer. from memory this is the tunnel piece and the left hand sill with the hand brake recess shape. i think also one of the pieces that was shaped t fit over wiring and relays behind one of the seats.

the drivers side floor piece had a kind of bituminous like black kind of backing. possibly a synthetic butyl material.
the passenger side floor piece had some sort of backing but was not as thick.
think passenger side sill piece was similar.

i still have all the original left hand drive carpet pieces from my 74.

i used a kind of closed cell foam sheet cut to shape and glued to the back of the carpet pieces i made for the floor to achieve a factory like fit for my right hand drive carpet set.
means the floor stampings do not show through the carpet. i had to glue down the sill pieces - no capability to heat form. and i sparingly glued down the tunnel piece in strategic spots to get it to hold its shape over the tunnel but i wanted to make sure i could get it up easily to access the tunnel for any maintenance issues. the tunnel piece is not glued down in the original factory carpets. and from memory the drivers side sill piece was not glued down or if it was it was very sparing and only in certain locations.

image of factory lhd carpets. you can see the various backing materials and types depending on position.

@StarBear has a 74 like mine and his factory carpets were identical in terms of varying material backing.