Abstract: A flexible spacer body has two opposing faces adapted to engage the inner surfaces of glazing structures to define an insulating glazing unit. The spacer body may be desiccated polymeric foam such as a silicone foam rubber or EPDM. An adhesive capable of bonding the spacer body to the glazing structure is carried by both of the faces. The adhesive may be from about 0.050 mm to about 1.524 mm thick. The adhesive material also has the properties of low argon gas and low moisture permeability. The adhesive comprises polymers where butyl rubber and/or polyisobutylene polymers together make up the majority of the polymers. The adhesive may also comprise other materials as needed to make it pressure sensitive and to impart a water resistant bond to glass glazing structures. The space assembly may include additional materials to secure the adhesive to the spacer body.