Machines designed to produce plastic bags or sacks are generally classified under heading 8477 (machinery for working rubber or plastics) rather than 8441. A combination machine capable of running both paper and plastic substrates requires a principal-use or essential-character analysis; importers should seek a CBP binding ruling if the machine's design does not clearly favor one material.

Both envelope-making and bag/sack-making machines fall within HTS 8441200000 — the heading explicitly covers all three product types. The distinction matters commercially (envelope machines typically handle lighter-weight paper with precision folding and gumming, while sack machines handle heavier kraft stock), but it does not create separate tariff lines at the US 10-digit level.