Meet the Dirty Dozen

The Dirty Dozen are 12 types of items that can mislead anyone trying to be a conscientious recycler. They seem recyclable, but are unwanted by recycling markets—and many contaminate the recycling process. 

Most of these items were never accepted for recycling in Mountain View, but often are placed in recycling by mistake. For example, only plastic bottles, tubs and jugs are accepted, yet people often try to recycle plastic bags, plastic drink cups, plastic clamshells and fruit baskets. Some items, like rigid plastic containers, were accepted for drop off at the recycling centers, but no more due to a decrease in market demand. Only certain kinds of plastic and paper are easily recyclable, and the market determines much of what can be recycled. Due to large amounts of materials, markets have grown more competitive.  

Since 2019, the Mountain View Recycling Center and the SMaRT Station are no longer accepting plastic bags, frozen food boxes, rigid plastics such as plant pots, pails, buckets and children's toys.

The Dirty Dozen guide will help Mountain View residents recycle right. The cleaner the recycling, the higher the value of the materials. The City’s recycling revenue offsets costs and can help to moderate trash rates. This handy at-a-glance guide to the Dirty Dozen flyer can be posted at your home or business. Each of the Dirty Dozen has a story about why it shouldn’t be placed in your recycling cart. Most of these items should go in your trash, unless an alternative is noted. 

This is Not Recyclable Because . . . 



Clamshells and similar thin plastic containers used to hold takeout food or produce like berries or baby spinach don’t melt down at the same temperature as other plastics in the recycling process. (Clamshells may have a separate or a connected (hinged) top and bottom.)  Although clamshells are made from the same PETE (#1) virgin plastic resin as soda and water bottles, they are manufactured using a "thermoform" process that gives them a more brittle, rigid form. Clamshells are also contaminated with labels attached with strong adhesives. Taken together, the labels, adhesives and thermoform characteristics make clamshells undesirable to plastics remanufacturers. 

Black Plastic

There is no market demand for black plastic. Why? (1) Black microwave trays, like clear clamshells, don’t melt well with other plastics in recycling facilities; (2) Black plastic is often contaminated by food residues; (3) Optical sorters used in many recycling facilities cannot “see” black items, so they cannot be easily sorted; and (4) Because they contain black pigment, black plastics can only be made into black items. Recycling firms prefer clear plastic, which can be dyed many different colors.

Plastic Wrap & Bags

There is no market for plastic bags and packaging wrappers (such as those around toilet paper or paper towels) from households because so much of the material is contaminated with moisture, food, paper receipts, etc. Plastic bags and packaging also wrap around machinery shafts and clog equipment at the SMaRT Station®. This causes costly shutdowns while maintenance staff cut the plastic off the equipment and send it to the landfill.

Egg Cartons

Whether made of clear or foam plastic or molded paper, egg cartons cannot be recycled in our area. There is no recycling market demand for clear or foam plastic or molded paper cartons. Because of the risk of spreading bird flu from chicken eggs to the carton, Asian markets (beyond China) no longer accept paper cartons. (Paper egg cartons are accepted in the City of Mountain View Food Scraps Program in the compost cart if you are an eligible subscriber.)

Alternative: If you know someone who raises chickens, give them your cartons for reuse. If you compost in your backyard, add paper egg cartons—they will break down in a well-managed pile.

Hot & Cold Cups

Paper cups for coffee or tea have a waterproof barrier that prevents them from breaking down at a paper recycling mill (similar to “Frozen Food Boxes” below). There is little recycling market demand for plastic cups for iced tea and other cold drinks because they don’t melt down well with other plastics. Likewise, the lids and straws from hot or cold cups also are not recyclable.  (Paper cups and paper straws are accepted in the City of Mountain View Food Scraps Program in the compost cart if you are an eligible subscriber. Hot & Cold cups marked "compostable" are not accepted in compost because they do not break down in the three month time it takes to compost food scraps.)

Frozen Food Boxes

Frozen and refrigerated food boxes like pizza boxes and butter boxes can’t be processed with other paper pulp at the mill because they are designed not to break down when wet. They are moisture-resistant by design. The exception is aseptic cartons for milk, juice, etc. Members of the National Beverage Carton Council started accepting aseptic cartons as recycled feedstock to demand the supply they create in the marketplace.

Takeout Containers

Whether made from paper, plastic or foam, lack of market demand for these materials, along with contamination from food and liquids, are reasons why takeout containers should be placed directly in the trash. Takeout cups, lids and straws also cannot be recycled. (Paper and other fiber-based takeout boxes can be composted.) 

If there is food in the containers, be sure to empty it into a food scraps collection container (if you live in a single-family home).

Padded Envelopes

Most padded envelopes contain non-recyclable materials such as plastic bubbles that make them unsuitable for processing into new paper products. Even fiber-based envelopes labelled as recyclable often contain gluing agents or other components that paper mills won't accept for recycling. Please place padded envelopes in the trash.

Food & Liquids

Empty liquids and food from recyclable containers before recycling them. Food left in containers contaminates other recyclables. Placing a liquid-filled plastic bottle in your recycling will prevent it from being recycled. Bottles are mechanically sorted from other materials by density. Plastic bottles containing liquid get sent to the glass sorting line. It causes costly delays to pull them out, empty them and place them with other plastics, so these bottles get discarded.

Be sure to empty food from all containers into a food scraps collection container. See


Items made from plastic foam, such as “styrofoam” packing peanuts, meat trays and other packaging materials, are mostly made of air. They contain so little plastic that recyclers find it’s not worth the expense of hauling and processing to recycle these items. That’s why there is no market for them.

Read the Mountain View ordinance banning foam plastic food and beverage containers at

Alternative: Bring clean packing peanuts to your local shipping store for reuse. Put the foam drink cup, foam takeout box, foam meat trays in the trash, and buy yourself a reusable cup and to-go box.  

Ceramics, Glassware

Different types of glass are made using different chemical recipes of sand, soda ash and additives. Factories in our area, while capable of recycling glass bottles and jars, cannot recycle other types of glass, such as drinking glasses, cookware, window panes and light bulbs. Ceramics are stone, not glass, and contaminate the recycling process.

Propane, Butane Cylinders


Even a small amount of leftover propane or butane creates a serious risk of explosion, fire and injury to waste collection and recycling workers. If the cylinders slip past quality control checkpoints at the recycling facility, they can explode when compressed in bales of metal.

Alternative: Bring these items to a hazardous waste event. Visit the Santa Clara County Household Hazardous Waste program to learn more.

Other Dirty Players and Problems

Diapers, greasy pizzeria boxes, household batteries, shoes and textiles are other offenders that should not go in the recycling cart.  For more information on how to dispose of specific items, visit You may also contact or call 650-903-6311.