The sample has arrived. It's about 3mm thick, softish hand, looks coarser than it feels, has a fair amount of stretch across what I assume is the weft and on the bias, and noticeably less on the warp. However, the ability to stop wind passing through is basically non-existent. For comparison, my Swanndri Ranger shirt is about the same, while the Bush Shirt has some noticeable resistance (but is by no means windproof). I can't imagine that it would shed rain for long - the fibres in the BushShirt are much more tightly packed.
As an insulating lining inside a windproof shell, I dare say it might be okay, but it seems rather expensive (£20.65 a metre, 140cm wide) for the fabric that it is. I don't get why they show pictures of it made into jackets - performance-wise, it strikes me as a non-starter for an outer shell.
I don't get the knitted Loden thing, either. Every reference I can find about Loden (it's history, etc) seems to mention, at least in passing, that it's woven and not knitted. I'm beginning to think that this is just some sort of knitted wool that's been fulled and is being called Loden when it really isn't.
I also got a sample of this...
https://www.myfabrics.co.uk/103-poso-g18-083_mottled-wool-fabric-grey.html
Slightly thinner at about 2.5mm, woven, similar hand, slightly softer feel. Stretch in all directions is similar to the less stretchy direction of the 'Loden'. Wind resistance is similarly non-existent. Expensive at £22.55 a metre (140cm wide).
As an aside, I also got some samples of cottons...
https://www.myfabrics.co.uk/81-04795-124_decor-fabric-canvas-dark-green.html
A very bluey green (like a mix of phthalo green and phthalo blue for those that paint pictures). Wind resistance is pretty hopeless.
https://www.myfabrics.co.uk/04-canvas140-036_canvas-140-cm-17.html
A passable forest green. Mostly cotton (20% polyester). Wind resistance also pretty hopeless.
https://www.myfabrics.co.uk/81-2888-027_cotton-twill-olive.html
The correct colour. Wind resistance is okay, although I've encountered better (comparable to, or slightly less than, a 100% cotton 5.11 Tactical shirt). Enough resistance to need to take care that it's carefully over the mouth when blowing through, and then some does get through with a decent 'huff'. I'd imagine a two-layer garment made of this would be as windproof as it gets. Hand is maybe a bit soft and drapey - strikes me as a good lining material inside a slightly stiffer shell (and comes in a decent range of colours if you want contrast).
Density of weave of the cottons increases in the order above. Stretch is similar for all - virtually none on the warp and weft, some on the bias.