Aluminum Bottle Caps

These aluminum bottle caps are built for product makers who want a clean, premium-looking closure without the guesswork. Available in black and silver finishes, they're PE-lined aluminum screw caps sized from 18-400 up to 33-400 — fitting Boston round glass bottles from 0.5 oz all the way through 16 oz. If you're running a product line with multiple sizes, you can stay consistent across every format.

Browse by neck finish: glass bottles that pair with these caps are available throughout the store, and all caps ship wholesale in box quantities of 600 units per size. Black aluminum caps and silver aluminum caps are both stocked — pick the finish that fits your brand.

What Are Aluminum Bottle Caps Used For?

Aluminum screw caps show up across a wide range of product categories because they hit a rare combination: they look expensive, weigh almost nothing, and hold up in shipping. The most common uses are cosmetics and skincare (serums, facial oils, toners), essential oil blends, tinctures, aromatherapy products, and any liquid formulation that benefits from a clean, professional finish. They're also popular with brands building private label lines where the packaging has to look retail-ready from day one — a matte black aluminum cap on a frosted Boston round reads premium in a way that a plastic cap simply doesn't.

Understanding Neck Finish Sizes

Every cap in this collection is labeled with a neck finish designation like 18-400, 20-400, 24-400, or 28-400. The first number is the diameter of the bottle opening in millimeters. The second number (always 400 here) refers to the thread style — it's a continuous thread, meaning the cap screws on and off smoothly in one motion. Match the cap's neck finish to your bottle's neck finish and you'll have a secure, leak-resistant seal. If you're not sure which size your bottles take, check the product listing for your bottle — the neck finish is listed in the specs.

Why Aluminum Over Plastic?

Plastic caps work fine for plenty of applications. But when the goal is brand perception, aluminum wins. It resists corrosion, doesn't crack under pressure, and has a weight-in-hand quality that signals quality to end customers. The PE liner inside each cap creates a clean seal against the bottle's land area — no leaking, no chemical interaction with the product. And because aluminum is fully recyclable, it fits naturally into sustainable or eco-conscious brand positioning without any greenwashing stretch.

Who These Are For

• Skincare and cosmetics brands bottling serums, facial oils, toners, and light moisturizers in Boston round glass
• Essential oil and aromatherapy producers who want a non-dropper closure option that still looks premium
• Tincture and herbal supplement brands needing a simple, secure cap for amber or frosted Boston rounds
• Private label companies building cohesive product lines where every detail of the packaging is intentional
• Food and specialty beverage brands using glass bottles for oils, vinegars, syrups, or infused products
• Craft and cottage producers selling at farmers markets or direct-to-consumer who need packaging that doesn't look small-batch

Frequently Asked Questions

What sizes do these aluminum bottle caps come in?
The collection covers neck finishes from 18-400 (fits 0.5 oz Boston round bottles) up through 33-400 (fits larger formats up to 16 oz). Each cap listing specifies the exact neck finish and the bottle sizes it's compatible with. Box quantities are 600 units per size.

What does the PE liner do?
PE stands for polyethylene — it's the white foam liner inside the cap that presses against the top edge of the bottle opening when the cap is tightened. It creates a clean, leak-resistant seal and provides a basic chemical barrier between the product and the aluminum. PE liners are a good fit for most cosmetic and essential oil applications. If you're bottling something highly acidic or chemically aggressive, contact us to confirm compatibility before ordering.

Do these caps work on Boston round bottles?
Yes — Boston round glass bottles are the primary bottle these caps are designed for. The 18-400 fits 0.5 oz Boston rounds, 20-400 fits 1–2 oz Boston rounds, 24-400 fits 2–4 oz Boston rounds, and 28-400 fits 4–8 oz formats. Always verify the neck finish on your specific bottle before ordering.

What's the minimum order quantity?
Caps are sold wholesale in full box quantities — 600 units per box. There's no smaller minimum. If you'd like to try a cap and bottle combination before committing to a full box, check out the samples collection.

Do you offer custom colors or finishes?
Currently, aluminum bottle caps are available in black and silver. For custom color or branding options, the custom printing page covers what's available for print and label customization on glass bottles and packaging.

How fast do these ship?
All orders ship within 3–5 business days from our US warehouse. We ship to US addresses only. Over 5,000 customers have ordered from The Bottle Depot since 2018, and every order comes backed by our satisfaction guarantee.