diff --git a/components/nif/data.cpp b/components/nif/data.cpp
index 29b11bd806..a134749bdc 100644
--- a/components/nif/data.cpp
+++ b/components/nif/data.cpp
@@ -247,16 +247,11 @@ namespace Nif
 
     void NiVisData::read(NIFStream* nif)
     {
-        mKeys = std::make_shared<std::map<float, bool>>();
-        uint32_t numKeys;
-        nif->read(numKeys);
-        for (size_t i = 0; i < numKeys; i++)
+        mKeys = std::make_shared<std::vector<std::pair<float, bool>>>(nif->get<uint32_t>());
+        for (auto& [time, value] : *mKeys)
         {
-            float time;
-            char value;
             nif->read(time);
-            nif->read(value);
-            (*mKeys)[time] = (value != 0);
+            value = nif->get<uint8_t>() != 0;
         }
     }
 
diff --git a/components/nif/data.hpp b/components/nif/data.hpp
index 1ccd2919b7..4000055e8c 100644
--- a/components/nif/data.hpp
+++ b/components/nif/data.hpp
@@ -193,8 +193,8 @@ namespace Nif
 
     struct NiVisData : public Record
     {
-        // TODO: investigate possible use of BoolKeyMap
-        std::shared_ptr<std::map<float, bool>> mKeys;
+        // This is theoretically a "flat map" sorted by time
+        std::shared_ptr<std::vector<std::pair<float, bool>>> mKeys;
 
         void read(NIFStream* nif) override;
     };
diff --git a/components/nif/nifkey.hpp b/components/nif/nifkey.hpp
index 5a755c8d0d..e32ef76d95 100644
--- a/components/nif/nifkey.hpp
+++ b/components/nif/nifkey.hpp
@@ -3,7 +3,7 @@
 #ifndef OPENMW_COMPONENTS_NIF_NIFKEY_HPP
 #define OPENMW_COMPONENTS_NIF_NIFKEY_HPP
 
-#include <map>
+#include <utility>
 #include <vector>
 
 #include "exception.hpp"
@@ -46,7 +46,8 @@ namespace Nif
     template <typename T, T (NIFStream::*getValue)()>
     struct KeyMapT
     {
-        using MapType = std::map<float, KeyT<T>>;
+        // This is theoretically a "flat map" sorted by time
+        using MapType = std::vector<std::pair<float, KeyT<T>>>;
 
         using ValueType = T;
         using KeyType = KeyT<T>;
@@ -78,8 +79,12 @@ namespace Nif
             uint32_t count;
             nif->read(count);
 
-            if (count != 0 || morph)
-                nif->read(mInterpolationType);
+            if (count == 0 && !morph)
+                return;
+
+            nif->read(mInterpolationType);
+
+            mKeys.reserve(count);
 
             KeyType key = {};
 
@@ -90,7 +95,7 @@ namespace Nif
                     float time;
                     nif->read(time);
                     readValue(*nif, key);
-                    mKeys[time] = key;
+                    mKeys.emplace_back(time, key);
                 }
             }
             else if (mInterpolationType == InterpolationType_Quadratic)
@@ -100,7 +105,7 @@ namespace Nif
                     float time;
                     nif->read(time);
                     readQuadratic(*nif, key);
-                    mKeys[time] = key;
+                    mKeys.emplace_back(time, key);
                 }
             }
             else if (mInterpolationType == InterpolationType_TCB)
@@ -115,8 +120,9 @@ namespace Nif
                     nif->read(tcbKey.mBias);
                 }
                 generateTCBTangents(tcbKeys);
-                for (TCBKey<T>& key : tcbKeys)
-                    mKeys[key.mTime] = KeyType{ std::move(key.mValue), std::move(key.mInTan), std::move(key.mOutTan) };
+                for (TCBKey<T>& tcbKey : tcbKeys)
+                    mKeys.emplace_back(std::move(tcbKey.mTime),
+                        KeyType{ std::move(tcbKey.mValue), std::move(tcbKey.mInTan), std::move(tcbKey.mOutTan) });
             }
             else if (mInterpolationType == InterpolationType_XYZ)
             {
@@ -132,6 +138,8 @@ namespace Nif
                 throw Nif::Exception("Unhandled interpolation type: " + std::to_string(mInterpolationType),
                     nif->getFile().getFilename());
             }
+
+            // Note: NetImmerse does NOT sort keys or remove duplicates
         }
 
     private:
diff --git a/components/nif/particle.cpp b/components/nif/particle.cpp
index d81d423fb6..9249541717 100644
--- a/components/nif/particle.cpp
+++ b/components/nif/particle.cpp
@@ -676,12 +676,16 @@ namespace Nif
 
     void NiPSysEmitterCtlrData::read(NIFStream* nif)
     {
+        // TODO: this is not used in the official files and needs verification
         mFloatKeyList = std::make_shared<FloatKeyMap>();
+        mFloatKeyList->read(nif);
         mVisKeyList = std::make_shared<BoolKeyMap>();
-        uint32_t numVisKeys;
-        nif->read(numVisKeys);
-        for (size_t i = 0; i < numVisKeys; i++)
-            mVisKeyList->mKeys[nif->get<float>()].mValue = nif->get<uint8_t>() != 0;
+        mVisKeyList->mKeys.resize(nif->get<uint32_t>());
+        for (auto& [time, key] : mVisKeyList->mKeys)
+        {
+            nif->read(time);
+            key.mValue = nif->get<uint8_t>() != 0;
+        }
     }
 
     void NiPSysCollider::read(NIFStream* nif)
diff --git a/components/nifosg/controller.cpp b/components/nifosg/controller.cpp
index 7e4c5da7a0..ee3d0dd45e 100644
--- a/components/nifosg/controller.cpp
+++ b/components/nifosg/controller.cpp
@@ -374,7 +374,8 @@ namespace NifOsg
         if (mData->empty())
             return true;
 
-        auto iter = mData->upper_bound(time);
+        auto iter = std::upper_bound(mData->begin(), mData->end(), time,
+            [](float time, const std::pair<float, bool>& key) { return time < key.first; });
         if (iter != mData->begin())
             --iter;
         return iter->second;
diff --git a/components/nifosg/controller.hpp b/components/nifosg/controller.hpp
index 468668ce76..41c8027eea 100644
--- a/components/nifosg/controller.hpp
+++ b/components/nifosg/controller.hpp
@@ -54,7 +54,8 @@ namespace NifOsg
                     return mLastHighKey;
             }
 
-            return mKeys->mKeys.lower_bound(time);
+            return std::lower_bound(mKeys->mKeys.begin(), mKeys->mKeys.end(), time,
+                [](const typename MapT::MapType::value_type& key, float t) { return key.first < t; });
         }
 
     public:
@@ -99,8 +100,8 @@ namespace NifOsg
 
             const typename MapT::MapType& keys = mKeys->mKeys;
 
-            if (time <= keys.begin()->first)
-                return keys.begin()->second.mValue;
+            if (time <= keys.front().first)
+                return keys.front().second.mValue;
 
             typename MapT::MapType::const_iterator it = retrieveKey(time);
 
@@ -116,7 +117,7 @@ namespace NifOsg
                 return interpolate(mLastLowKey->second, mLastHighKey->second, a, mKeys->mInterpolationType);
             }
 
-            return keys.rbegin()->second.mValue;
+            return keys.back().second.mValue;
         }
 
         bool empty() const { return !mKeys || mKeys->mKeys.empty(); }
@@ -283,7 +284,7 @@ namespace NifOsg
     class VisController : public SceneUtil::NodeCallback<VisController>, public SceneUtil::Controller
     {
     private:
-        std::shared_ptr<std::map<float, bool>> mData;
+        std::shared_ptr<std::vector<std::pair<float, bool>>> mData;
         BoolInterpolator mInterpolator;
         unsigned int mMask{ 0u };