We're currently renovating our house from 1978 and don't know whether we should go with stone wool, glass wool, or polystyrene. Energy prices are still high and we want to do it right. What would you guys recommend?
For your old building renovation, I'd recommend stone wool - it's got good thermal performance, is relatively cheap, and handles being near welding better if you ever need that.
Fiberglass works too, it's just a bit itchy to work with. Polystyrene is cheaper, but for a proper renovation in 2026 I'd go more for the mineral fibers because they're just more durable and deal better with old building structures.
But the most important thing is that you seal the joints properly and don't have any thermal bridges - you'll save more money on that in the end than by picking between materials.
At our place we went with rock wool for the roof insulation and I'm really happy with it, but it really depends on exactly where you want to insulate.
For the exterior walls of an old building from '78 I'd rather go with XPS or polystyrene, because the wall behind it stays drier - rock wool absorbs moisture and that can be problematic with older houses. Glass wool is honestly the cheaper option, but you have to be careful when working with it, some people don't like it. Get someone to advise you on-site beforehand about which solution works best for your specific wall structure, that'll save you headaches later.
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