Lock&Lock 20-Fluid Ounce Square Food Container， 2-1/2-Cup Detailed Features Patented Blocking Hole System Lock&Lock Classic Consistent flow of resin--does not produce a weld line along the hinge.<br>Inconsistent flow of resin--produces a weld line over time.<br>Lock&Lock Classic lids feature four side flaps or "wings" that are hinged and slightly flared at the end for an easy grip when opening.<br>More importantly， they come with holes (rectangular-shaped openings) that line up with matching knobs on the base of the containers， making it easy to latch the lid to the base， locking it into place.<br>This patented blocking hole system maintains the integrity of the lid and helps promote an easy， tightly locked container.<br>Lid's 4 wings come with holes that line up with base Weld line does not form around the hinge piece Hinge is designed to be short in length to prevent stiffness when opening and closing Lock&Lock Classic Blue hollow-center silicon band in the lid helps create an airtight， leak-proof seal.<br> Special Silicone In addition to its blocking hole system， the Classic food-storage containers feature a blue hollow-center silicon ring in the lid that helps create an airtight， leak-proof seal. Generic silicon with a solid center doesn't compress as well and doesn't have the same restorative power as hollow-center silicon， which means an inferior seal.<br>Lock&Lock's hollow-center silicon seal delivers superior compression and restoration power that helps ensure an airtight seal.<br>Permeability When testing the freshness of foods， one of the most important factors is the permeability of the container.<br>In comparison to other brands， the permeability of Lock&Lock products showed to be drastically better.<br>