Introduction: Nalgene Straw Cap

I made this design to allow people that own nalgene bottles to use something other than the traditional cap and have options on how to drink out of the cap. I planned on originally 3D printing the cap, but after 6 failed attempts to print a cap I realized it was going to happen. The cap I made was created using a preexisting cap that I modified and made a mold of. My main struggles while designing this cap were printing the cap and getting the plastic mold to actually work other than that it was smooth sailing.

Step 1: Materials

For this project you will need the following items:

Nalgene Lid

Silicone Rubber Kit

Plastic Mold Kit

3D printer

Gorilla Glue

Exacto Knife


Hot Glue Gun

Metal File

Step 2: Remove Top of Nalgene Cap

Take an existing Nalgene Cap and cut out the top so that only sides are remaining.(A knife or drill are the best choices)

Step 3: 3D Print Lid

Using a 3D printer you're going to print a small part to fit on the lid

Step 4: Putting the Part Together

Take the nalgene lid and hot glue the 3d printed piece to it.(make sure there are no air holes)

Step 5: Making a Silicone Mold

Create a box out of foamcore and seal it a hot glue gun. Then suspend the cap in the box using a piece of hot glue. After that pour in your silicone mixture from one corner to make sure no air bubbles are created and wait for it to cure.

Step 6: Remove Foamcore and Cap

After the mold has cured remove the foamcore and cap from the mold.(Remove carefully so the mold doesn't tear)

Step 7: Fill the Silicone Mold With Plastic

After removing the cap you're going to reseal the mold using rubber bands then fill the mold with plastic. (Make sure to burp the mold while pouring to get rid of air bubbles)

Step 8: Remove the Lid

Once the plastic has dried you can remove the lid and check it for holes.

Step 9: Sand Rough Edges

Use a file or sanding tool to smooth away rough edges on the lid.

Step 10: Add Straw

Find a straw that fits in the small hole of the lid and use glue to seal it in place. I found that starbucks reusable plastic straws work best.

Step 11: Creating Seals for the Cap (Extra)

Using the silicone mold you made and a knife, you're going to cut out pieces of rubber that fit the mold.