In the past, virtually all fluorescence filters for microscopy were produced using a "soft coating" technology that is subject to degradation over time.  In fact, the vast majority of thin-film optical filters in the field today are soft coated filters.

Semrock offers exclusively hard-coated filters manufactured with ion-beam sputtering technology. The coating is deposited directly onto a single substrate, with no epoxy required. The simple all-glass structure and hard dielectric glass coatings (as hard as the glass on which they are coated!) mean they are virtually impervious to humidity and can be cleaned and handled like any standard glass optic.  All Semrock filters are coated on a single glass substrate, so there is never any adhesive in the optical path to autofluoresce, scatter light, or degrade with environmental or optical stress.  The result is exceptionally durable "no burn out"  fluorescence filters of the highest performance.

For more information on the benefits of hard coatings, please see Semrock's Filter Reliability Study.