# What is the key testing difference between AAMI Level 3 and Level 4 in medical protective fabrics?

> Source: https://breathablefilm.com/news/knowledge-center/aami-level-3-vs-level-4-testing-difference/
> Author: kh_sales02
> Published: 2026-05-05
> Updated: 2026-08-28

## Key takeaways

- AAMI Level 3 focuses on fluid resistance, tested via AATCC 127 (hydrostatic pressure) and AATCC 42 (water resistance), requiring the fabric to withstand at least a 50 cm water column.
- AAMI Level 4 goes further by requiring the fabric to pass ASTM F1671, the only level that guarantees a complete biological barrier against blood-borne pathogens and viruses.
- Because of this, Level 4 is reserved for high-risk surgical and infection-control environments, while Level 3 suits routine procedures with mainly liquid-splash exposure.

## Frequently asked questions

### What is the key testing difference between AAMI Level 3 and Level 4 in medical protective fabrics?

AAMI Level 3 focuses on fluid resistance, tested via AATCC 127 hydrostatic pressure and AATCC 42 water resistance, requiring the fabric to withstand at least a 50 cm water column so surgeons are protected from synthetic blood or saline splashes during routine procedures. AAMI Level 4 goes further by requiring the fabric to pass ASTM F1671, making it the only level that guarantees a complete biological barrier against blood-borne pathogens and viruses, not just liquid splashes, which is why it is reserved for high-risk surgical and infection-control environments.

### Does passing AAMI Level 3 mean a fabric also blocks viruses?

No — AAMI Level 3 only certifies resistance to liquid splashes under hydrostatic pressure via AATCC 127 and AATCC 42, it does not test for viral or blood-borne pathogen penetration. Only AAMI Level 4, which requires passing ASTM F1671, guarantees a complete biological barrier against viruses.