I have been diffusing my hair for years, (I live in MN afer all). I have very thick hair, and I would be drying my hair for hours if I didn't use high heat. The products I put on my hair seem to protect it from heat damage, as my hair never feels fried afterward (I diffuse about 2-3x/wk).
I am always trying to enhance my curls, so I find that starting my diffusing upside down really makes them spring up. It also gives volume at the roots. Then, for a shorter period of time I diffuse standing upright and leaning side to side. However, if I start off drying my hair standing up, and THEN finish drying upside down, I get fuzzy, big triangular hair!
I put my ionic hairdryer on high speed/ high heat for about 3/4 of my drying session, and then swith it to a low speed the rest of the time. I find that the longer I wait to diffuse my hair, and let it air dry, the fuzzier or frizzier it seems to get. So, it I'm plopping, I do it 15-20 min. tops to preserve curl definition. I let the bowl of the diffuser scrutch my hair, and I try to touch it as little as possible. I usually stop when hair is about 85% dry. Hopefully that all made sense. Good luck!
Co-wash: Hair One Argan Oil or Burt's Bees GreenTea and Fennel
Low-Po: Devacurl LP or SheaMoisture Black Soap(1-2x/wk)
Condish: SheaMoisture Deep Repair Mask
Leave-in: Kinky Curly Knot Today AND
Styler: GF Curl Construct Mousse or Biotera gel
Treatments: Oils or butters,and trying out Aubrey Organics GPB for protein