ISO 3384:2005 specifies two methods for determining the decrease in counterforce exerted by a test piece of vulcanized or thermoplastic rubber which has been compressed to a constant deformation and maintained thus at a predetermined test temperature. Two forms of test piece are permitted: cylindrical test pieces and rings. The use of ring test pieces is particularly suitable for the determination of stress relaxation in liquid environments. Testing at temperatures below standard laboratory temperature is not specified. The methods have been used for low-temperature testing, but their reliability under these conditions is not proven.