A material in Stockroom is something you buy and build with but never sell, tracked in the unit you count it in. It can live as a draft product in your Shopify store, or in Stockroom only - with no Shopify product at all. That keeps one inventory - the one Shopify shows - while letting recipes say "12.5 g of wax" and purchase orders say "3 pails of 5,000 g".
Create or mark a material
In Inventory > Products, switch the segment to Materials and click New material: name, Stock unit, a cost per unit, and an opening quantity. Stockroom creates a draft product in your store (draft, so it is never sold), tracked at your location in that unit. An existing product can become a material with Mark as material on its product page - pick the unit and it keeps its history.
Tick Keep this material in Stockroom only and no Shopify product is created: the material, its stock, its costs and the builds that consume it live entirely in Stockroom. That suits raw materials your store has no reason to list - resin, packaging, fabric by the metre. Everything else works the same: order it on purchase orders, receive it, count it, build with it. It just never appears in your Shopify admin.
Pick the unit small - grams rather than kilos, millilitres rather than litres - because stock counts are whole numbers in Shopify. Recipes take decimals in that unit (0.25 m), and Stockroom rounds across build records so nothing drifts.
Buy in packs
Set a pack size on the material's stock settings ("Pail = 5,000 g") and purchase orders work in packs while stock stays in the unit: the PO line says 3 pails of 5,000, receiving adds 15,000 g, and restock rounds to whole packs. The product page and PO line show the unit everywhere a quantity appears.
Where materials show
Everywhere a product shows, with its unit beside every quantity - inventory, the product page, bills of materials, builds, Restock, reports and CSV exports.
In the component picker of a bill of materials, like any other product.
On stocktakes, adjustments, transfers, reorder points and alerts - nothing is special-cased.
Good to know
The unit is stored by Stockroom, not Shopify - Shopify shows the plain count. Change it with Change unit on the product page.
A material that never sells has no sales history, so Restock looks at what builds consume rather than what sold; consumption-based reorder suggestions for materials are on the roadmap.
Un-marking a material (Not a material) keeps the product and its stock; it just stops showing the unit.