I was soooo happy to see the materials removed from Detect Magic in the new edition.
I don't know if I agree that a simple sealed paper envelope or a pocket is enough to prevent a 4th level detect magic from detecting an Orb of Gold Dragonkind or a Holy Avenger Longsword.
This rule also prevents the spell Detect Poison from detecting if the fluid in that stoppered vial or bottle is poison or not.
At my table, it will work regardless of material. (it does stink for Society players though)