Charcoal canisters are broadly used for radon detection because of their handiness and short sampling period. Radon detection using charcoal canisters are known to be susceptible to surrounding conditions such as temperature and humidity. Public radon inspectors cannot handle extreme temperature, and the relative humidity can differ in districts due to the use of different types of construction. Thus, if relative humidity can be controlled at the entrance of a charcoal canister, radon inspectors will be able to procure more reliable data. The purpose of this study was to assess the efficiency of existing filters in a charcoal canister and to apply a new type of filter (Super Absorbent Polymers, SAP) that can control the moisture penetrating into the charcoal canister. Based on adequate case studies using the new filter, radon data have shown over 98% close to the reference data irrespective of varying moisture levels. Meanwhile, basic filters showed 88% similarity compared to the reference data, which means that charcoal canisters were affected by moisture. The SAP filter is reasonably inexpensive and once it turns into its gel shape (which, in turn, is saturated by moisture), it can be easily replaced. This filter will not only be able to provide more accurate radon data, but also apply to other gas phase material detections that are sensitive to moisture in the air.