Called the Gift Of Nothing, the product is accompanied by the taglines "exactly what you asked for" and "less is more".
Julian Kirby, lead campaigner on plastics at Friends Of The Earth, said: "It's almost a riddle in itself.
"Who would actually want this, and who would buy it?
"The rest of the world sees the need for only the most essential plastics, with a fast phase-out of all other wasteful plastics, so let's hope folly like this goes unloved and doesn't re-appear."
Sian Sutherland, co-founder of anti-Plastic campaign group A Plastic Planet, added: "How can Poundland possibly think this is OK?
"This product is designed to go straight into the bin but will last for 500 years.
"It is a symbol of everything that is wrong with our view of the world. We are treating our beautiful planet like it is disposable when it is all we have."
Poundland defended the product as "a bit of fun", but did not clarify whether it could be recycled.
"Our customers love it as do loads of others online," the company said in a statement.
"They all know it's a bit of fun and we understand that's still allowed in moderation."
Shoppers have shared pictures of the product, some with complaints about its use of plastic.
"OMG just pointless plastic polluting packaging for literally nothing," tweeted former Countryfile TV presenter Julia Bradbury.
However, others have found the product amusing.