U.S. Military Specification MIL-C-26861

This specification classifies materials into classes and grades according to cushioning performance. Class numbers represent static loading ranges:

• Class 1 – Below 0.08 psi
• Class 2 – 0.08 - 0.2 psi
• Class 3 – 0.2 - 0.5 psi
• Class 4 – 0.5 - 1.0 psi
• Class 5 – 1.0 - 1.5 psi
• Class 6 – 1.5 - 4.0 psi
• Class 7 – 4.0 - 10.0 psi

Grade letters indicate maximum gs allowable for loading range indicated by the class number (24-inch multiple drop):

• Grade A – Less than 20 gs
• Grade B – Less than 40 gs
• Grade C – Less than 60 gs
• Grade D – Less than 100 gs
• Grade E – Less than 130 gs

To determine compliance, go to the cushioning curves. For example: What thickness of ETHAFOAM™ 220 polyethylene foam would meet the requirements of Class 4, Grade C?

• Class 4 has a loading range of 0.5 to 1.0 psi.
• Grade C = below 60 gs
• For ETHAFOAM 220 polyethylene foam, 24-inch multiple-drop curves show that thickness of 2 inches and higher stay below 60 gs over the 0.5 to 1.0 psi loading range and would, therefore, be acceptable.

Other property requirements in this specification are not detailed here. ETHAFOAM plank products currently meet the other property requirements in this specification.