4.1 Additional items of clothing
(a) A player may wear supports made of elasticated or compressible materials which must be washable.
(b) A player may wear shin guards which conform with World Rugby Specifications (Regulation 12).
(e) A player may wear shoulder pads which must bear the World Rugby Approval Mark (Regulation 12).
And a PDF of Regulation 12 is available online - all 32 pages of it.