Insulated wire thwn 2 gauge

I come across some thwn 2 gauge and somr other wire its black and stranded the thwn 2 gauge is white and it said nylon coating is it hard to strip with a box cutter? Whats the percentage of wire inside? I think its used for something called a cable tray? Im also gons be getting some wire that goes in a trailer its black and has four wire inside stranded heavy as crap. Tried to search thwn 2 gauge mothing about it came up ugh.