Siberian larch (Larix sibirica) is a slow-grown, resin-rich softwood known for tight growth rings and noticeably high density for a conifer. That slow growth produces hard-wearing boards with strong earlywood/latewood contrast and plenty of knot character.
In the UK it became especially associated with cladding because the heartwood offers decent above-ground durability without treatment, and the density gives crisp machined profiles. The same density also means fixings can be unforgiving—pre-drilling is often sensible—and movement/weathering still needs managing through detailing.
Siberian larch isn’t a “magic outdoor timber,” but it is a very capable one when installed correctly: ventilated backs, protected end grain, sensible gaps, and a finish strategy that accepts (or controls) greying. Done right, it’s a tough exterior softwood with a distinctive, hard-edged feel.