Fluffy towels

I think it might be the industrial size tumble dryers that commercial laundries use.

Despite the ads, I've never found fabric softener made any kind of difference to my towels so stopped using it years ago.

You could try adding water softener. Calgon is the well-known (and very expensive) brand but I use much cheaper powdered versions from Tesco or Sainsbury's - they call it something like limescale removal powder. You just add it to the wash with detergent. We have quite hard water so it does make a big difference but I've also used it in soft water and it still leaves things noticeably softer so probably worth a go whatever the water type.

I do find fabric softener helps too, but only a little bit of a brand that washes out nicely at the next wash, otherwise you get crusty old softener left in them which doesn't help and reduces their absorbency. I use Ecover.

If you have a tumble dryer, after trying it to start or finish towels off, I think it works best to start them off in the dryer - it seems to fluff up the fibres before they get 'set' by drying. I don't find they fluff up anywhere near as much if you just use the dryer at the end.

The other option is to look at the towels you have. Thin, poor quality towels may never go as fluffy as better ones. I don't think it's just about spending money though! The nicest ones I've had are ones from Tesco, the 'hygro' ones. I always start them in the dryer as that works best for them but even if completely air dried they still feel softer than other towels washed and dried in the same way.

Rinsing properly, vinegar in the last rinse, dryer balls in the tumble dryer.

Hotel towels are different to begin with as they are made to withstand vigorous use.
Then they are washed with no washing powder (like you buy in the supermarkets) or conditioner, and are tumbled dried at high heat.

I don't know the answer, but I quite like a rough towel. I feel they dry you better and buff your skin.

Generally they soften after one use in any case