Made of lightweight birchwood, these smooth needles by Knit Pro are grippier than metal so very useful if you are using a slippery yarn. Some people find them kinder to their hands than metal.
2.25mm is a great size for socks with a good, close fabric or for finer yarns. These DPNS are 20cm long.
Please note, the photo is a generic pic - they needles pictured are clearly larger than 2.25mm!