TL;DR - (1) don't be hypothyroid, (2) don't expect volume from an ionic hair dryer, (3) don't condition your roots, (4) try sulfate-free shampoo and/or vitamins but don't start with high hopes
I lurk often but rarely post. I save it for where it counts! And now I present: passionate opinions about getting the most out of thin, fine hair.
I have fine hair and A LOT to talk about here! Hair used to be thin, is much thicker now (see #3), is not "thick" by anyone else's standards. The individual strands are baby-fine and I have a lot of them. My hair is generally very soft, mostly straight but a little wavy, and does not hold a curl for anything. I get a sturdy ponytail with 3 wraps of a normal wrist-size hairband. I can always make 4 wraps but I rarely need the last one, and it will slowly slide down & out with only 2 wraps.
This is what works for me...
1) products: sulfate-free shampoo + no conditioner above the ears/ponytail - Brand is less important to me, although I like mid/high end lines like Living Proof, Kerastase (almost all of their shampoos have sulfates, bummer), Ouai... Speaking of Ouai, I like their Wave Spray pre-blowdry for some texture & grit that kinda keeps the strands airy rather than clumped together & flat. Texture Spray after blowout does this too. I use them together like this, but its a lot of fragrance. I'd say these products work better than most, they're my current favorites, but if the volume lasted as long as the fragrance, I'd be a customer for life.
2) styling tools: non-ionic blow-dryer + metal barrel round brush - I rank this #1 most important if (a) you use a dryer, and (b) your goal is more volume. Brush is minor here - I prefer metal for adding curl, i think natural bristles are too smoothing aka flattening. Back to dryers... ceramic heating is fine, avoid ions. Ions are framed as an upscale feature with no downsides, and no brand will tell you "avoid if you want volume!" Yes, negative ions are great for: shine, softness, minimizing damage, and silkiness... but all these goals are the opposite of volume. The sad truth is that you can't have it all (unless you want to decrease volume, then you can have it all). Dryers that are really heavy on the ions make adding volume & curl at the ends just hopeless. Ionic output is a trial & error thing, I wish you luck. I haven't been able to find any technical specs or measurements that aren't muddled with marketing buzzwords (Ulta is actually the worst for this). This is great timing... In the last few weeks, I've tried & returned 4 dryers: 3 ionic and 1 non-ionic. I got great volume from the non-ionic dryer (Elchim Milano), but it was too heavy & the low speed was not low enough for me. If you read reviews on ionic dryers (pretty much all high-end like T3, GHD, Chi, Elchim, BabylissPro, even Hot Tools) and ignore complaints about price or malfunctions, the poor reviews will complain that the hair falls flat & they can't get volume or curl. They often blame lack of heat, but I suspect ions are actually at fault. The great reviews will praise the smoothness & sleekness & control they get over their unruly hair. In conclusion, I feel very strongly about this and I wish brands would make this clear in their product descriptions. Ionic dryers great for everything EXCEPT adding volume. In fact, they are good for removing volume so hair can lie flat & smooth. I doubt there exists a volumizing or curl-holding product that can overcome this, sadly. I am a product junkie, I feel like I've tried them all. For more volume, its less about the product, and almost entirely about the dryer & drying process.
3) health: thyroid problems - If this applies to you, then it beats the dryer for #1 most important. Thin hair is one of many common symptoms of a hypothyroid (hypo = too slow, hyper = over active). Hypothyroidism sucks. Symptoms are ALL over the place, and no single symptom really stands out as a red flag (except maybe a slight goiter). If you have more than a few symptoms AND you've been brushing them off for a while (excuses like: I should sleep more... exercise more... be less lazy... eat better... try harder... work harder... cut this or that from my diet) please consider going to the doctor about it. The blood test isn't a super expensive one, and the medication is cheap & easy and your whole quality of life will improve. For me, the big symptoms that resolved with treatment were low energy all day, difficulty waking up, difficulty concentrating, 10-15 pounds weight gain, thin & brittle hair & nails. I still have to put in effort, but treatment at least opens the door for better outcomes. Nails still get flakey, hair no longer weak & brittle, and it grew in thicker over time.
4) hair+skin+nails vitamin - this one's a slow burn. there's a lot to choose from, and it can be tough to know exactly how much help they bring. could be worth a shot. I think I had good results from a fairly inexpensive brand, but its really hard to say for sure because I was trying a lot of things to get better hair.
Wow this got long, I guess I had a lot of emotion bottled up on this subject! I hope it was at least helpful. I hope someone can benefit from my years of disappointing trial & error!
PS - the dryers I tried & returned....
Non-ionic - Elchim Milano - only blows high & higher speed. made my hair so tangled during the upside-down rough dry, then blasted it off my round brush. Feels super heavy after a few min.
Ionic - Babyliss Nano-Titanium & Babyliss Rapido - the ions weren't super heavy, I could have lived with either except the low speed setting is still way too much air flow. These are lightweight and not super loud but each one had a motor that sounded weird.
Ionic - Sephora Blast - amazingly gentle low speed setting, very quiet & lightweight. Its perfect except for the darn ions from this one were the worst of all. This would be an amazing dryer for someone that wants minimize volume & doesn't have a ton of hair. For me, it was the nicest to use, but gave the worst results of the group.
