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Zeta II Overview/Sizing

Notice: The Zeta II® helmet liner has been superseded by the new Zeta III™ helmet liner.
Click here to order the new Zeta III helmet liner
PM Air Warrior Approved: The lightweight Oregon Aero® Zeta II® Helmet Liner was tested by the U.S. Army Aeromedical Research Laboratory and provides the same benefits as the Oregon Aero® Zetaliner® Helmet Liner. Zeta II® was designed for maximum comfort, protection, and helmet stability. Helmet liner is self-wicking to dissipate perspiration and keep you cooler. Your Zeta II® Helmet Liner is easy to fit, install, and maintain. Helmet Liner is equally effective while wearing Night Vision or other externally mounted equipment.
Choosing your Zeta II Liner Length

Step 1: Choosing Your Zeta II® Helmet Liner Length

Use this guide and the tables below to determine which size Zeta II® Helmet Liner is right for you. Measure the inside of your HGU-56P helmet from front to back — down through the bowl — as shown in the photo. Make a note of this measurement, then follow Step 2 to determine the liner thickness you need.

Step 2: Choosing Your Zeta II® Liner Thickness

The Zeta II® Helmet Liner for the Military HGU-56P is available in four thicknesses: 1/4", 3/8", 1/2" and 5/8". The most common thickness we sell is 1/2". To determine the correct thickness liner for your helmet, refer table below.

NOTE: If your TPL® (Thermo Plastic Liner) has been heated and fitted, you will probably need a Zeta II® Helmet Liner one thickness thinner than listed below.

Zeta II® Helmet Liner Thickness Table

If your TPL® Liner Has... Then try a...
2 Layers 1/4" Liner
3 Layers 3/8" Liner
4-5 Layers 1/2" Liner
5+ Layers 5/8" Liner

Once you have found the length and thickness you need, choose your Zeta II from the table below.

The sizing charts on this page are intended to suggest a starting point for the fitting process. Each individual should be fitted for comfort and stability. Results may differ from the data shown here. Oregon Aero is committed to helping you select the proper Zeta II® Helmet Liner. If you have any questions call us at 800-888-6910.

Zeta II® Size Table for Military HGU-56P(Click the part number# to order)

15" Styroliner (Internal Measurement front to back) Helmet Size
1/4" Thick #9A-0015-101 NSN 8415-01-580-5456 XS/XXS
3/8" Thick #9A-0015-102 NSN 8415-01-580-5460 XS/XXS
1/2" Thick #9A-0015-103 NSN 8415-01-580-5465 XS/XXS
5/8" Thick #9A-0015-104 NSN 8415-01-580-5480 XS/XXS
16" Styroliner (Internal Measurement front to back) Helmet Size
1/4" Thick #9A-0016-101 NSN 8415-01-580-5484 S/M
3/8" Thick #9A-0016-102 NSN 8415-01-580-5489 S/M
1/2" Thick #9A-0016-103 NSN 8415-01-580-5492 S/M
5/8" Thick #9A-0016-104 NSN 8415-01-580-5494 S/M
17" Styroliner (Internal Measurement front to back) Helmet Size
1/4" Thick #9A-0017-101 NSN 8415-01-580-5498 L
3/8" Thick #9A-0017-102 NSN 8415-01-580-5499 L
1/2" Thick #9A-0017-103 NSN 8415-01-580-5500 L
5/8" Thick #9A-0017-104 NSN 8415-01-580-5859 L
18" Styroliner (Internal Measurement front to back) Helmet Size
1/4" Thick #9a-0018-101 NSN 8415-01-590-3520 XL
3/8" Thick #9a-0018-102 NSN 8415-01-591-3013 XL
1/2" Thick #9a-0018-103 NSN 8415-01-591-3015 XL
5/8" Thick #9a-0018-104 NSN 8415-01-591-3020 XL
Oregon Aero Zeta-II Installation
The Oregon Aero® Zeta II® Helmet Liner being installed in a Military HGU-56P Aviation Helmet.
Oregon Aero Zeta II Helmet Liners

Easy Installation and Care

Your Oregon Aero® Zeta II® Helmet Liner is installed in 4 easy steps using hook/loop fastner strips. Complete instructions are included with the liner. If you would like to see how easy the Zeta II® Helmet Liner is to install you can Click here to download installation instructions in PDF format.

Cleaning Instructions: Hand wash your Zeta II® with mild soap and rinse thoroughly. To dry, place your helmet liner flat on a large towel. Fold the towel over to cover liner. Use a rolling pin or similar object to squeegee out the excess water. Do not wring liner. Re-Shape your Zeta II® Helmet Liner and allow it to air dry in a warm place or in front of a fan. Do Not Use Any Artificial Heat Source to Dry. Unless conditions are humid, your liner should dry overnight.

Note: Wringing your Zeta II® or drying it with an artifical heat source will damage the liner. Use recommended methods of care only.