D3O is a great replacement product for older gear whose armor is decaying, become stiff or is too old to be rated and tested like modern armor.
You can buy pairs for shoulders, elbows, knees and hips. Back pads are also available. All are sold in two "levels". The two levels have the same shape, length and width, but the higher level units, "level 2" are about 50% thicker.
Any of the D3O pieces are all made out of the same material... an energy absorbing compound that is soft, pliable and flexible... which means comfortable!
The D3O is BY FAR the best selling replacement armor on the market.