J Channel
J Channel is a building material that is usually made out of vinyl or plastics. Sometimes it can be made out of metals such as aluminum or tin, but these days that is getting rare.
There are many uses for J-Channel. It can be used to hold ceiling panels in place, used as a drip edge for areas that you want to keep dry, and in extreme cases, can be used as bottom tracking for mobile home skirting.
The most extensive use of J-Channel is for trimming vinyl siding around doors and windows. This use is not just for mobile homes and it can be used on just about any building structure.
The Bad Part
Oh yeah, this stuff is great. When used properly, it can make a window look good or correct how a crooked door looks. It basically covers up builders mistakes. But there are just some mistakes that J-Channel cannot cover up. Addtionally, there are mistakes that can be made with J-Channel that can drastically damage the home that it is installed on.