What’s the difference between a SealLine dry bag and a SealLine packing system sack?

Dry Bags
Dry bags come from the paddlesport world. They are made from heavy-duty materials that withstand the stresses of exposed, demanding use in or around wet, aquatic environments. Dry bags are frequently used by paddlers (e.g., canoe, kayak, raft, SUP), though they are increasingly used on land in circumstances where their durability and protection against the elements are beneficial.

Packing Systems
Packing system sacks come from the camping/backpacking world and are typically made from lightweight or ultralight materials. They are meant to be put inside a larger pack or bag, providing selective water protection and/or organization for specific items (e.g., sleeping bag or clothing) with minimal overall weight penalty.