THICKNESS 1/8", 3/16" or 1/4"? Depends on the underlying surface condition and whether it's flat or round... plus your budget. 1/4" is stiffer and lays flatter — for a "more-level" appearance. 1/8" is more likely to eventually take the shape of any underlying holes and protruding rocks. However, if you fill in the manger holes and rough spots with lime, sand or ready-to-mix concrete, 1/8" will lay almost as level as 1/4", and will probably last as long as you are farming.
1/8" is more pliable, and is easier to install over curved surfaces, such as round/curved mangers and auger trough. However, 1/4" can be made more flexible by "conditioning" it in a very-warm room (such as a heated milkhouse) or in direct sunlight. Unroll liner for quicker heat absorption. After liner has "relaxed", simply step on it to press liner into your curved/round manger or auger trough.
1/4" is recommended on conveyor and barn-cleaner chain applications up to 30" wide. Because 1/4" will lay flatter, it is less prone to hump and become worn or torn by chain riding over it. 1/8" or 3/16" is recommended in manure-spreader and other chain applications over 30" wide.
WIDTH Because poly is very slippery (especially when wet), allow space for walkway beside manger liner. 30" provides easier cleanup of feed pushed out toward walkway, plus more floor protection from feed acids. 24" is popular if aisle space is limited, and also with budget buyers. Holddowns will reduce spillage into feed alley by up to 90%.
Width of liner should be narrower than conveyor or gutter. The extra side clearance will allow poly to expand lengthwise when warm, without binding against side-walls and humping. Order liner 1/8" narrower up to 13" wide, and 1/4" narrower over 13" wide. If necessary, liner width can be quickly narrowed for your special application, using a table saw.
LENGTH Rolls vs sheets are ordered by over 97% of our manger-liner customers... because rolls are quicker and easier to install. Also, rolls are seamless for easier sweeping (no cracks for moisture or feed to spoil in). Rolls recommended for conveyors up to 13" wide. Install as two pieces if conveyor is longer than 50'. Use 20' sheets for conveyors over 13" wide.