'radiation-permeable' is a compound formed in English from 'radiation' + 'permeable'. 'Radiation' ultimately comes from Latin 'radiare'/'radius' meaning 'ray', and 'permeable' comes from Latin 'permeabilis' (from 'per-' meaning 'through' and a root meaning 'to pass').

'radiation' entered English via Medieval/Scientific Latin (radiatio/radiation-) influenced by French and Latin usage and developed into the modern English 'radiation'; 'permeable' came into English from Latin 'permeabilis' through French (perméable) and Middle English adoption, and the compound 'radiation-permeable' is a modern English technical formation combining the two.

Originally 'radiation' referred to the action or process of emitting rays and has kept that technical meaning; 'permeable' originally meant 'able to be passed through' and retains that sense. Combined, the compound now specifically denotes something that allows radiation to pass through.