Can papers of the same grammage be swapped in a shopping bag?

Not without validation. Grammage describes mass per square metre; thickness, grain direction, surface and bonding behaviour can still differ. When reviewing PALETTE coloured paper or IMPRINT coated paper, first assess colour, artwork and creases, then make a complete bag in the intended design. Ask the converter to check the base, seams, handles and reinforcement with the actual contents and use conditions. Record the grade, grain direction, adhesive and processing sequence. Revalidate a paper change rather than carrying over the previous material’s load rating.