Short answer: Yes, moksha/siddhashila is considered matter-free in Jainism.

Explanation in simple terms:

• The cycle of birth and death happens because a jiva (soul) is bound by karma. Until all karmic bonds are burnt, the soul takes many births.
• Moksha is the complete removal of all karma, resulting in a liberated soul. A liberated soul is formless and beyond the cycles of birth and death.
• Siddhashila is the realm where liberated souls reside after attaining moksha. It is described as a pure, non-material, formless state. In this realm there is no further bondage or propulsion of karma, and no physical birth or death.
• Different Jain traditions (Digambar and Shwetambar) may differ in emphasis or in how they describe certain details, but both agree that siddhas are liberated souls beyond material existence.

Key point to hold: the presence of siddhas in siddhashila does not imply matter in the sense that can bind karma; it represents a pure, non-material state beyond the cycle of karma.