Photo etch are small detail bits made out of metal sheet. They do small detail bits in metal because resin/plastic just can't get that thin without breaking. Photo-etch often needs to be bent... and is generally glued on with CA (Super Glue). Personally, I hate PE, since I always lose the pieces and never can get the pieces where I want them... and i end up using too much CA and have my hands stuck together at the end.