Flightgear On-Line, the website for the collector of military flightgear

Helmet fitting systems
editted by: Ron Kraan, Steen Hartov

Type	Reference helmet	Fielding status	Attributes
Foam pads	APH-5 APH-6 HGU-2/P HGU-2A/P early HGU-26/P	No longer used	Various pad thicknesses accommodated variable head sizes. Comfort dependent on user.
Three-strap sling	HGU-2A/P(G) HGU-2A/P-D SPH-3 SPH-3B SPH-4	Some SPH-4 still in use	Individual strap adjustment provided user adjustability. Comfort difficult to achieve, some individuals experience significant discomfort, others had no problems. Attachment clips contributed to SPH-4 impact attenuation.
Thermoplastic Liner (TPL^TM)	SPH-4 SPH-4B Later HGU-55/P HGU-56/P Others . . .	Currently fielded	Widely accepted in the aviation environment. Can be individually fitted by heating. Can be cleaned. May adversely affect helmet stability. Durable.
Pads, mesh, & drawstring	IHADSS	Currently fielded	Difficult to comfortably fit the IHADSS helmet. May degrade helmet retention if too many pads are used to obtain comfortable fit.
Thermofit Liner (TFL^TM)	Various SPH and HGU types	Special cases	Currently used by USAARL when comfortable fits cannot be attained with the standard issue TPL^TM. Performance still under evaluation.
Foam in place	HGU-33/P SPH-3C later HGU-26/P early HGU-55/P	Not used by the Army	Provides an individual fit with little adjustment tolerance. Provides a stable fit, can become uncomfort-able if helmet is not repositioned to original fitting location. Difficult to obtain consistent foam density. Could affect impact attenuation performance.
Silicon foam fill	developmental	Proposed	Provides an individual fit. Pliable to relieve pressure points after redonning the helmet. Durability, operational performance, and user acceptability are unknown.
Epoxy coated foam	developmental	Proposed for Comanche helmet	Provides a stable, individual fit. Can become uncomfort-able if not repositioned to original fitting location. Durability, operation performance, and user acceptability are unknown.
Custom foam fit	U.S. Navy fixed-wing night attack helmet. In it's original form used in HGU-33/P	Operation	Provides a stable, individual fit. Requires a wax mold of the aviator’s head be taken. Liner custom made to casting made from wax mold, at manufacturer’s plant. Lengthy time process. Method originally developed by Sierra corp. using plaster strips for making molds of aviators head.