Aim: Packages that are wet after steam sterilization are identified as a failure in the sterilization process. The objective was to investigate whether different fabric loads and packaging materials affect temperature and humidity inside the packages after steam sterilization. Materials and methods: Four groups of instrument packages containing either metal instruments alone or various types of fabric load (cotton, towel, or a combination) were prepared with three different packaging materials (cotton fabric, nonwoven material, or paper-film). The packages were then subjected to a full cycle steam sterilization at 121°C for 20 minutes. Percent humidity and temperature were determined immediately after removal of the package from the sterilizing chamber, and after every 15 minutes to 1 hour. Results: The presence of any fabric inside the packages significantly increased intrapackage humidity immediately after removal from the sterilizing chamber. Intrapackage humidity dropped sharply in the packages containing metal alone or towel. The presence of cotton fabric inside the packages retained higher intrapackage humidity at every time point. The packages with metal alone had a significantly lower temperature compared with the other three groups when measured immediately. Intrapackage temperature gradually decreased in time. There was no difference in temperature between the groups from 15 minutes. The packages wrapped in cotton fabric significantly retained immediate intrapackage humidity compared with nonwoven materials or paper-film pouch. Conclusion: Packages containing cotton fabric retained intrapackage humidity; and this may cause sterilization failure. Clinical significance: Our data provided evidence to support that cotton fabric should not be included in the package of metal instruments for steam sterilization in routine dental instrument processing protocols.