PET bottles are typically clear, but can come in a variety of colors. However, even with coloring, PET bottles have a glossy reflection on it's surface. If clear, it is completely transparent. It's popularly used for beverage drinks because it's lightweight and durable. PET is also popular for the colored, but clear pill bottles often used for supplements. All #1 PET bottles are BPA free (they never have BPA in them to start with).

HDPE bottles are typically either white or opaque (non-transparent / cloudy), but can also come in a variety of colors. Due to it's higher density, you can't completely see through the plastic. HDPE is popular in a variety of industries from food & beverage to chemicals due to it's durability and strong barrier properties so you don't end up drinking sour milk. All #2 HDPE bottles are BPA free (they never have BPA in them to start with). 

The majority of PVC is actually used for pipes, but there is still packaging out there made of PVC due to it's clarity and durability. PVC packaging has a glossy surface and can come in different colors. If clear, it is completely transparent.  Aesthetically, it has very similar properties as PET.  However, PVC has a rep of being the 'poison plastic' because it can release toxins at higher temperatures. This also causes a problem in the recycling stream because it contaminates the rest of the recyclables. With so many negative aspects, it's best to avoid this plastic as a consumer product!

LDPE is a flexible material than can made into rigid products such as packaging. Rigid LDPE products are flexible (or squeezable) and most commonly an opaque color similar to HDPE. However, as everyday consumers, we encounter the flexible version of LDPE most often in the form of plastic bags and wraps. It's the grocery bag, storage bag, stretch wrap, bubble wrap (they're little bags of air!), trash bag etc. that are all mostly made from LDPE.

Even though you may see the #4 and recycle symbol, bags and wraps cannot go into your curbside recycling bin! This means you shouldn't put all your recyclable bottles into a bag and dump the whole bag into your curbside bin! Bags can get caught in the sorting machines at recycling facilities and break them down. Instead, there are local dropoff locations specifically for #4 LDPE bags. You can find the closest dropoff location at how2recycle. Make sure you're sorting your #4's correctly!

PP looks similar to HDPE where they are typically white or opaque (translucent/milky), but can also come in a variety of colors. Due to it's density, you cannot see through PP containers. However, PP is the most common material used for caps you find on bottles, jars, etc. PP is also used for straws which has gotten such a bad reputation that cities have banned the use of them! People go so far as saying that straws can't be recycled, but there just may be a way.

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Regardless of size or shape, the PP material is not accepted at all recycling facilities. It is a challenge for facilities to accept #5 because it is cheaper to make #5 plastic than it is to recycle it. Remember, check with your local recycling before you toss #5 into the bin!

PS has a range of properties depending on what form it is in. In it's rigid form, PS is popular because it mimics the look of glass. It can be clear and hard, but more durable and lighter than glass, so it's a popular choice in the cosmetic industry. Plastic utensils and red solo cups are also made of PS. It's extremely rare for recycling facilities to accept these forms of PS due to not being cost effective, but it doesn't hurt to check.

The other form of PS we are familiar with is styrofoam. Styrofoam is also a very unfriendly plastic due to releasing toxins at melting temperatures which also can contaminate the recycling stream. Thus the styrofoam form cannot go curbside. However, there are efforts to close the loop with new companies such as Styro-Go (source).

Plastics are categorized as #7 if they are made of any of the #1-6 plastics. Since these plastics have no true classification, they are considered contaminants in the recycling stream. BPA plastic (the notorious plastic in baby bottles that is harmful to humans and the environment) is also classified as a #7. Another type of #7 are acrylic jars. Tubes are a bit difficult because they can be made of #2 HDPE, #4 LDPE, or something in between! Because tube material is so difficult to determine, it often is sorted as #7 aka trash. However, not all #7 is terrible.

A new resin called PLA is a corn-based and marketed as biodegradable. Since this resin is new, it is automatically classified as a #7. However, special facilities must process PLA in order to truly compost. So overall #7 is just very confusing and will probably end up in the landfill.