The disadvantage of thin aluminum is that it does not offer much insulation, which means that condensation can build on the outside of the bottle when cold drinks are transported, and hot drinks will result in a bottle which cannot be comfortably touched. Sigg sells insulating sleeves that protect the bottle from dents, help insulate the beverages inside them and eliminate the condensation issue. The limited size of the opening also makes it difficult to fill or clean the bottle or to use it for purposes other than drinking, though Sigg now makes wide-mouth bottles, and adapters that allow the use of the standard-size caps. Aluminum bottles are also more prone to dents than stainless steel bottles. Another disadvantage is that the bottles are unsuitable for freezing its contents, as freezing liquids expand in volume and cause the bottle to crack. Therefore, it is advisable not to keep fluids in the container during extended periods below freezing temperatures.