Ethylene-vinyl alcohol copolymer (EVOH) is the highest-performance oxygen barrier resin in common packaging use. But "EVOH" is not one material: commercial grades span roughly 29 to 44 mol% ethylene, and that single parameter drives the balance between barrier performance, flexibility and processability.
The ethylene-content trade-off
As ethylene content rises, the resin becomes more flexible and more thermoplastic, but its oxygen barrier drops. Lower-ethylene grades (29-32 mol%) deliver the lowest oxygen transmission rates (OTR) and the best aroma retention, but are stiffer and more humidity-sensitive. Higher-ethylene grades (38-44 mol%) offer deeper draw, better thermoformability and stronger moisture tolerance, at the cost of barrier performance.
Matching grades to applications
- 29-32 mol% (e.g., EV2951F, EV3201F, EV3251F): non-retort multilayer films, flexible packaging, cereal and snack bags, pharmaceuticals and cosmetics where maximum OTR reduction is the priority.
- 32-38 mol% (e.g., EV3251FT, EV3851F): retort pouches, hot-fill and aseptic structures, and processing windows that demand stability at high line speeds.
- 38-44 mol% (e.g., EV4405F, EV4451F, EV-4451V): rigid containers, bottles and deep-draw thermoformed trays where forming behavior and impact resistance dominate.
Reading the numbers on a TDS
Two specifications matter most when screening an EVOH grade. First, OTR at standard conditions (typically 20°C / 65% RH) tells you the barrier ceiling — but remember that humidity sharply increases OTR, so retort and hot-fill structures need grades tested under relevant conditions. Second, melt flow index (MFI) predicts line behavior: higher MFI grades run faster on cast and blown film lines, while lower MFI grades suit sheet and thick co-extrusion.
Structure design notes
EVOH is hygroscopic and must be sandwiched between polyolefin or PET layers — direct contact with water-based products or humid environments degrades barrier over time. Typical structures include PA/EVOH/PE for retort pouches, PE/EVOH/PE for flexible films and PET/EVOH/PE for bottles. A tie-layer resin such as Bynel or Orevac is required to bond EVOH to the structural layers.
POLYVALA supplies SK Chemical EVASIN EVOH grades covering the full 29-44 mol% range, with technical data sheets, batch COA and sample quantities available for evaluation. Contact our team for grade recommendations matched to your film or container structure.