Flimsy stuff mostly rejected by one wanting firm material (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Reversal of ( … rejected ) “lace”(flimsy stuff/a fine open fabric) minus its last letter ( mostly ) plus ( by ) I(Roman numeral for “one”) plus ( wanting ) CO(abbrev. for “company”, a commercial firm).