Greetings from Finland. I'd go for foam glass bubbles for easy application and healthy result.

here is first link about the stuff in English.

>GEOCELL Foam Glass Bubbles are versatile, insulating beads for use with or without a binder (such as natural hydraulic lime or cement). In addition to having no negative impact on health, using foam glass bubbles guarantees excellent insulation with the highest fire safety and ease of use.

Thermal Conductivity – 0.07 W/mK.

Supplied in 100 litre bags.

2-4 mm size beads.

LOOSE FILL THERMAL INSULATION

GEOCELL® foam glass bubbles have excellent free-flowing properties due to their spherical shape. As a result, the small glass beads easily fill voids in beamed ceilings, floors and cavity walls for improved thermal insulation. Furthermore, it’s very easy to cover pipes and cable ducts. Use environmentally friendly, lightweight glass bubbles in many of the same applications as vermiculite but in addition have the significant advantages of being:

non-absorbent.

non-capillary.

vapour permeable.

fire resistant Class A1

inert, safe and dust-free.

made from recycled glass (not produced from virgin materials).