SF2 Filter Cap for SHT2x Digital Humidity & Temperature Sensors The SF2 filter cap, from Sensirion, has been designed to protect the SHT2x series of digital humidity & temperature sensors. The filter cap protects them from particle contamination, dust, water immersion and consequent condensation when being mounted. Composed of PBT and a filter membrane, the filter cap has been manufactured to ensure that the response time for humidity measurement is barely impacted.