There is an alternative glass to AN glass. Durst is using this glass on their negative carriers for optimal sharpness. I am not sure but it may be something akin to Denglas (coated anti reflective glass). I believe that they will provide this glass separately. Seems that a glass kit for my 138S was up near $85.00 US as I recall.
Originally Posted by Sean
On a separate note, I have used glassless carriers before. I have found that glass neg carriers provide optimal sharpness especially for condensor type enlargers.