Finding the Right Fit

The Ultimate in Flying Comfort™

The original ZetaLiner® Helmet Liner and the PM Air Warrior approved Zeta II® Helmet Liner both solve the problems of liner hot spots, perspiration and helmet instability — safety-related problems which can reduce focus and execution of the mission.

Easy Helmet Liner Fitting
No more hour-long fitting sessions that require liner heating! The ZetaLiner® and Zeta II® Helmet Liner Upgrades can be done in minutes as shown below. See the following information about how to select the correct ZetaLiner® or Zeta II® Helmet Liner length and thickness.


PM AirWarrior Approved Zeta II Helmet LinerWhen installed, the Zeta II® Helmet Liner should be level with the lower edge of the polystyrene liner at the front of the helmet, fit smoothly along the interior contour of the polystyrene liner and mate completely with the hook and pile tape sewn into the rear nape pad of the helmet.

ZetaLiner® Helmet Liner Installation Instructions

Zeta II® Helmet Liner for HGU-56P
Brochure & Installation Instructions

How to Select the Correct Helmet Liner Length and Thickness


Choosing a Helmet Liner LengthMeasure the inside of your helmet from front to back, down into the bowl, as shown in the photo. Then consult the chart below and find the correct part number.



Choosing a Helmet Liner Thickness
Both liners comes in four thicknesses: 1/4", 3/8", 1/2" and 5/8".  The most commonly used thickness is 3/8". To select the proper liner thickness, review the information below, then find your part number. NOTE: If your TPL®* has been heated and fitted, you will probably need a Helmet Liner one thickness thinner than those listed below.

NOTE: The sizing informaton above is intended to suggest a starting point for the fitting process. Each pilot should be fitted individually for comfort and stability. Final results may differ from the above data. Fitting only takes minutes!


ZetaLiner Product listing
Zetaliner Product listing
18" Zeta II® Helmet Liner

#9A-0018-101 Zeta II® Helmet Liner          1/4" thick:  NSN  8415-01-590-3520

#9A-0018-102 Zeta II® Helmet Liner          3/8" thick:  NSN  8415-01-951-3013

#9A-0018-103 Zeta II® Helmet Liner          1/2" thick:  NSN  8415-01-591-3015

#9A-0018-104 Zeta II® Helmet Liner          5/8" thick:  NSN  8415-01-591-3020



*SPH-4®, SPH-4B®, SPH-5® and TPL® are federally registered trademarks owned by Gentex Corporation. Use on this web site of these trademarks is made for reference purposes only. Oregon Aero has no business affiliation with Gentex.