Electronic HPDs are available in both earmuff and custom earplug styles. In 1954, an earmuff with a more comfortable cushion design was developed. Workers may want to wear their hearing aids under an earmuff. It is also notable as the home of Chester Greenwood, who invented the earmuff. There are different earmuff style options for HPD users. It is possible for sound to transmit through the earmuff materials, reducing the device's effectiveness. Earmuff HPDs typically consist of two ear cups and a head band. Greenwood invented the earmuff at age 15, obtained a patent for it in 1877. Earmuff style hearing protection devices are designed to fit over the outer ear, or pinna.