Being from Florida I did not have to worry about thermals while fishing but now that I live in upstate South Carolina it gets rather cold. I understand now the importance of layering. My question is this, what kind of rated thermals should I be using? Right now I have grade 1.  

I mainly fish Lake Hartwell. All responses appreciated. Happy fishing

I am a little north of you and do quite a bit outside in the cold, and very cold.

Columbia omni heat is very good.  Thin, warm, comfortable, breathable and wicks moisture off my skin.

https://www.columbia.com/technology-omniheatreflective/

A-Jay 

I use Simms ExStream Core thermals.  It's the only kind I've worn that don't feel like they're squeezing me. They feel more like sweatpants and T-shirt, but aren't that loose and baggy.  And they'll keep you super warm.

When I was working and traveling monthly from SoCal to cold northern regions I wore Eddie Bauer Silk long underwear. Comfortable in temperatures from our warmer climate and severe cold climates. 

Tom

If you are a costco member they have some nice no name stuff that works and is cheap.  32 degrees is the brand,  2 pack of shirts or pants for about $15

I'm from Northern Ma just below the NH line. Which I believe is colder than So. Carolina.  I use Cold Gear and yes its pricey but I've owned mine for over 10yrs so they last.  I've never been cold with these on even when smelt fishing in Central Maine, matter of fact they're so warm if I spend any time in the house with them on I start sweating, they wisk away moisture, are very light wgt, but they are tight like spandex which some people don't like.

Try polypropylene and come back and thank me......it's what I was issued in the military, great stuff.

I am a fan of wool blend union suits.

As long as you remember  that "cotton kills" you'll be fine.

Just match that first layer with your activity level.

For low level activities a thicker base layer is recommended