Firm or extra firm pillows may help to alleviate tight arm pain experienced by 'side' sleepers. An extra firm pillow better supports the head -without flattening out- to help fill the distance between the ear and shoulder, explains WebMD.
With support between the ear, side of the face and the outside shoulder, less pressure is applied to the shoulder and arm. Such pressure often causes arm pain due to the unnatural, constant stress applied to the rotator cuff and may also cut off circulation to cause numbness, according to WedMD. The most highly-sought pillows with extra firm support are typically buckwheat-filled or made from memory foam or latex, mentioned by QPillow.