Of course, ordinary glass, including the heat resistant varsities like borosilicate ( e.g Corning Pyrex Brand) and fused silica, are limited in the amount of radiation they can pass at wavelengths longer than about 2 to 2.5 micrometers (microns). They are essentially opaque at wavelengths longer than abort 3.7 microns.
Fortunately there are a wide range of other materials that can pass infrared, even at wavelengths as long as 14 microns. Unfortunately, as it turns out, the other materials have widely varying optical properties (some are opaque in the visible), hardness, solubility in water and price.
Therefore to choose an optical window or lens material for a specific application is often a job of tradeoffs. Knowing the optical properties of the materials is a first step.
To see a concise list of potentially usable infrared window and lens materials plus some key properties of each, including spectral transmission, click here to visit the Lawrence Berkeley Labs web page.
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