In effect as of September 2014, 510-521 17A/B Head Cushions have been shipping with outer shells of durable, nylon based material with a webbing strap added to strengthen the mounting snaps. Velcro® has also been applied to the exterior for attachment of the head cushion foam spacer (HCFS, p/n 525-745). The same improvements have been in use successfully in the field for our other head cushion, 510-754, change reference Bulletin #4 of 2012.
Bulletin 4 2012 New-Improved Products Bulletin.pdf

Note: Proper fit of the head cushion is important and critical to both comfort and safety. In general, the head cushion should be snug fitting which will help hold the helmet to your head. The head cushion should also be adjusted so that it assists in the proper seal of the oral nasal mask to the face.
Please contact your local KMDSI dealer or e-mail KMDSI at [email protected] for more information.