The sleeve is a thermoplastic elastomer, not silicone
Which is why it is soft, why it is porous, and why it cannot be boiled.
The insert is a thermoplastic elastomer: a plastic that behaves like rubber when cool, melts when hot, and is softened with oil. The maker calls its own blend SuperSkin and does not publish the recipe, but the class of material is not in doubt, and it explains the handling rules better than any instruction leaflet does.
Two things follow straight from the chemistry. It is porous at a scale you cannot see, so it cannot be sterilised and it belongs to one person for its whole life. And it softens with heat, so hot water, a dishwasher or a microwave deforms it permanently. Silicone, which is a different material entirely, tolerates all three.
What to do with it
Three rules follow from the material, and all three are about heat and oil. Warm water only, never boiling, never a dishwasher and never a microwave. Water-based lubricant only. And store it dry and loose, not squeezed into a drawer where it keeps a fold for months.
When buying, the material should be named on the box. A soft toy sold with no material declared is the one case where the price is not the main difference.
What the material means for the body is on the guide's page about strokers and their materials.
