That would be a sweater made of possum yarn, not a sweater for an opossum. 

From the Nordic Yarn site:

Possum Fibres from New Zealand
Some facts that you may not know about the possum from New Zealand:

  • Possums are not native animals to New Zealand
  • They were first introduced from Australia in 1837, and have no natural enemies
  • There are approx. 60 million possums in New Zealand, reproducing at 30% per year
  • It is considered a pest, destroying native plants, animals and birds in New Zealand’s environment
  • Possums eat and destroy nearly 20,000 tonnes of vegetation – every night!
  • The NZ Government spends NZ$90 million a year just on eradicating the possum
  • Within New Zealand, both the Ministry of Agriculture and Fisheries, and the Department of Conservation and Regional Health Boards support the humane culling of possum numbers as a key means of protecting NZ’s unique eco-systems

The Possum fibre is:

  • 55% warmer than merino
  • 35% warmer than cashmere
  • shown to have a high resistence to pilling compared to other natural fibres
  • exceptionally soft to the touch
More information and some photos of possum sweaters at Supreme Possum Merino.