The hottest item in Philly is a DOG MASK ... with costume shops throughout the city scrambling to stock up so fans can wear K9 heads to the NFC title game this weekend.
TMZ Sports spoke with the 5 top costume shops in the Philly area ... and they've all said their phones are ringing off the hook asking about the masks Chris Long and Lane Johnson wore to celebrate their "underdog" victory over the Falcons.
One shop in particular -- Masquerade -- says they've already gotten 20 calls about the masks before the store even opened this morning (plus 10 fans who came to the store in person), and now they're working to get a shipment before Saturday.
Derek Lee of D&J Costumes and Entertainment says the makers of the exact German Shepherd mask Long and Johnson wore are all sold out ... so the store has ordered masks from other breeds in case fans wanted to branch out.
Some of the stores are worried about the timing -- because if the dog-mask shipments come in after Sunday (and if the Eagles lose) ... they'll be screwed!
As we previously reported, the Eagles are encouraging fans to wear dog masks to the stadium on Sunday -- as long as they remove them when going through stadium security.