A 2D bag is two film layers sealed at the perimeter. Empty, it is flat; full, it becomes a pillow. Small 2D bags — 3 L and below — are the workhorse for buffer, sample and intermediate holds because they fill fast, drain almost completely and store flat.

 

Their limitation is hydrostatic pressure. A tall pillow of liquid puts the seam under load, and the highest stress sits at the corner where the seal turns. Large 2D bags therefore need a support tray, and they should never be lifted by the film.

 

 

A 3D bag has a formed base, so it stands in a bin or on a pallet and holds a defined volume with a defined footprint. Harmake's 3D range covers 100 L at 740 × 540 × 300 mm, 200 L in two footprints, 250 L, 500 L in two footprints and 1000 L at 1100 × 1080 × 940 mm.

 

 

• Volume accuracy. The footprint fixes the fill height, so the volume is reproducible.

• Handling. The bag sits in a rigid container and can be moved by pallet truck or bin lift.

• Mixing. A cubic geometry gives better bulk mixing than a pillow when the bag is agitated or recirculated.

 

The cost is that a 3D bag needs its container. A bag without a bin is a bag waiting to burst.

 

 

 

The film in Harmake's storage bags is a five-layer co-extrusion at a nominal 0.325 mm, with a ULDPE product-contact layer, polyethylene structural layers and an EVOH barrier. The published physical data is what a storage specification should be built on:

 

Over a 30-day hold at 2 to 8 °C, oxygen ingress through the wall oxidises sensitive components and water loss concentrates the buffer. A plain polyethylene bag is adequate for a shift; an EVOH-containing film is what makes a month-long hold defensible. The lower the temperature, the slower the chemistry — but the film still governs the total flux.

 

 

Cold break below −45 °C tells you the film survives freezing. It does not tell you the bag survives freezing. Ice expands, and a bag frozen in a rigid bin with no headspace will split at a seam regardless of film grade.

 

Freeze with headspace, freeze flat where the geometry allows, and thaw slowly in a controlled environment rather than in a warm water bath that shocks the weld.

 

 

 

For −80 °C and liquid nitrogen work, a standard storage bag is the wrong product. Harmake supplies cryopreservation bags built for those temperatures, with the tubing and port configuration suited to a cryogenic workflow. The rules are strict: fill to the rated volume, leave expansion space, use the specified rack, and never handle a frozen bag by the tubing.

 

 

 

A storage bag is only as good as its access points. Harmake's storage bags are configured with TC25 sanitary clamps, Robert clamps, needle-free sampling valves, MPC quick connectors and C-FLEX tubing, and each bag is integrity tested before release.

 

 

• Sampling from the bottom. A needle-free valve on a dip tube at the base gives a representative sample; a valve on a side port near the top gives you the liquid that has been sitting in the tubing.

• Vent path. A storage bag that will be drained needs a sterile vent, or it will collapse and trap product. A bag that will be filled needs a vent, or it will balloon and stress the seams.