I have a grammar which says that:
"The 'noun+noun' structure is normally used to say what things are made of."
"A few pairs of nouns and adjectives are used as modifiers with different meanings. Generally the noun simply names the material something is made of, while the adjective has a more metaphorical meaning."
a gold watch – golden memories;
a silk stocking – silken skin
I've also heard that the "-en" ending is used in a poetic sense. But when I looked up at my dictionary for the word "wooden", it brought as an example "wooden bench"; even though "wooden" wasn't being used in a figurative nor in a poetic way. Furthermore, I don't know whether to use "wood door" or "wooden door", meaning that the door is made of wood.
Best Answer
With regard to "wood" and "wooden", part of the choice depends on whether the "woodiness" of the object is fundamental or incidental. The door is perhaps the best example:
I might say "Go down the hallway and then go through the wood door on your left" when giving instructions. The door is wood, but I'm just describing it, the same way I might say "green door".
On the other hand, I might say "On the front of the cathedral is a massive wooden door." In this case, "wooden" is a part of the image of the door -- it's more than just an incidental characteristic.
For a bench, one would generally say "wooden bench", since "wooden" is more fundamental to the nature of a bench than to a door. But "wood bench" might be used if, eg, there were two similar benches side-by-side, one metal, one wood, and you merely wanted to identify which.
I suspect that this difference applies to several other "-en" choices, though I haven't considered them very much.