If you're looking for a drop in bed liner then you'd notice the Duraliner truck bed liner as one of the more prominent brands. It compares with the Pendaliner also made by Penda. Here's how it works and what to watch for.
This is a really inexpensive option for protecting a bed of a pickup. As you can see from looking at liners or even looking at pictures, this is a custom molded piece that has built in deep grooves to get the water out of the truck. Note also that it includes cut-outs for fitting the various tie-downs and such that are peculiar to each model of truck.
Note also that this liner comes as either an over the rail or under the rail model. This is a pretty typical drop-in bed liner. It is quite light in weight but certainly suitable for normal use in most trucks.
Here's what to watch for though.
All those cut-outs and the way the liner fits at the rails are openings for water to get under and behind the liner. As long as that water makes it to the drain holes in the bed there is not trouble at all. What happens if holes get clogged or the path to the drains is blocked under the plastic? Then you have pools of water under the liner and a potential disaster.
What's even more troublesome is the potential for all those edges and opening to serve as wind catchers that can shift the liner around in the bed. If that happens, and it often does, then you often get worn spots in the bed paint under the liner. This is the major potential downfall of all these types of liners as compared to the spray in bed liner.
That brings up the whole spray in liner vs drop in bed liner debate. It also suggests the Dual Liner truck bed liners which uses rubber on the floor rather than plastic. It's a lot more expensive though.
The Duraliner truck bed liner has a lot to recommend it. It's cheap and easy to put in. It can be removed, unlike spray in bed liners. The material could be heavier but it still is quite tough. What you have to watch for is water behind the liner and a loose liner that will wear the bed paint.