Sennheiser PX 100 Collapsible Headphones for $25.94 shipped. Here is a screenshot for your reference. The Sennheiser PX 100 Headphones feature a slim, lightweight design. The ear cups can be turned 90 degrees and closed up, then put into its carrying case that can fit into a shirt pocket. At the time of this post, 929 out of 1019 user reviews have given it 4/5 and 5/5 ratings. Most places have it for about $49 or more.