PLA + is greatly improved PLA with a great ease of printing
PLA PLUS is mechanically stronger or can withstand higher temperatures or has better resistance to sunlight and moisture than regular PLA. PLA PLUS is therefore functional, but simply prints like PLA as usual.
HTPLA is High Temperature PLA and can withstand much higher temperatures than normal PLA. You usually have to bake the 3D prints from HTPLA in the oven for good temperature resistance. At Plasticz you can order TREED Shogun PLA, FILOALFA ALFAPRO and ALFAPLUS.
PLA PRO is a type of PLA that is UV resistant - and weather resistant. In addition, it is harder and has good resistance to high temperatures. PLA PRO has the most complete features of all PLA series. Plasticz sells ALFAPRO; a UV-resistant PLA that also has good moisture and high temperature resistance.