apparatus for joining cohesive coated plastic sheets in a closed peripheral pattern with bulging of at least one sheet within the closed peripheral pattern to provide a sealed compartment containing only a gas such as air , or foam , under superatmospheric pressure . a method for forming a sealed bulging compartment containing substantially only a gas at superatmospheric pressure comprises joining two cohesive material coated sheets by engagement of said portions of said cohesive material coating at a closed periphery while causing at least one of the sheets to be bulged by gas at superatmospheric pressure . a bulging sealed cushion formed of two sheets each coated on one side with cohesive , air impervious material , at least one of the sheets being bulged outward , and containing substantially only a gas at superatmospheric pressure .