Can these be used in walking (hiking) boots?

I don’t have hiking shoes. So, I don’t know. I use them for past 3 years… great with Sketchers casual shoes. With gym shoes not so much. This insole is quite thick. Can take a lot of space if the shoe is low ankled etc… Anyway, fully recommend and it helped me a lot with my plantar fasciitis

Are these supposed to feel as though you have a golfball under your insole? Thanks.

Helps the heal and arch mend to stop the pain, will cause a little uncomftable to start with until fofft mould into them. My man has had Plantar insoles for a while now and he no longer complains of the heal pain. The last time he had plantar he could not walk with out pain for a year as that is how long it took to fix. So now, as he plays lots of golf, as soon as he feels it comes on he uses Dr Scholl's insoles.

Can these be used in sandals ?

It's a very tricky question. I guess if the sandals are closed enough I mean the insoles could stay in while you are walking then it could work. I have been using them in closed toes footwear like shoes or boots. Personally my opinion is a no for sandals. You have to find some alternative options for sandals. I can recommend some arch support sandals for wear rather than insoles. Hope it's helpful.