I read a story posted here not too long ago about how dealers spray glass on their bud to increase the weight. The expert they interviewed for this was a doc of some kind, and he basically said that the tiny glass particles were too large to pass into the lungs because they were something like 0.005 microns, and only partifles 0.003 microns can pass into the lungs. He said using a filter would completely eliminate any possibility of any glass passing into your lungs. I would assume that menthol is similar if not larger in size, so I'd use a filter at the very least.